This Week in Microbiology

With Vincent Racaniello, Michele Swanson, Michael Schmidt, and Dickson Despommier

Episode 168: The lesser of two weevils

Aired January 4, 2018

TWiM 168: The lesser of two weevils

Vincent: This Week in Microbiology is brought to you by the American Society for Microbiology at


Vincent: This is TWIM, This Week in Microbiology, episode 168, recorded on December 28th, 2017. Hi everybody, I am Vincent Racaniello and you are listening to the podcast that explores unseen life on Earth. Joining me from Wadsworth, Illinois, Michael Schmidt.

Michael: Hello everyone!

Vincent: People may be wondering why you are in Wadsworth. You’re visiting.

Michael: I’m up at, I’m visiting my brother the fireman and his family for the holidays so I came up and have been freezing ever since I got off the plane. Yesterday it was -5 for the high during the height of the day. Today has warmed up a whopping 10 degrees, it is actually 5 degrees now.

Vincent: You’re talking Celsius, aren’t you?

Michele: No.

Michael: Well, no, I’m talking Fahrenheit.

Vincent: Seriously? That is really cold. I thought it was cold here.

Michael: Yesterday I went up to Green Bay to see my nephew and his family and it’s a two and a half hour drive north of where I’m at, and its high yesterday was -5 and it was very, very cold. When we were drivign up it was -9 in the car. Fahrenheit.

Vincent: It’s -8 Celsius here, I thought that was cold, but wow. You’re way below that.

Michael: Oh yeah, it’s a wonderful thing.

Vincent: Joining us from Ann Arbor, Michigan, Michele Swanson.

Michele: Hello! Where it is a sunny 12 degrees Fahrenheit or -11 degrees Celsius.

Vincent: You don’t dip in the minus Fahrenheits there, or maybe you do.

Michele: This morning when I woke up it was -3 Fahrenheit. But it is sunny and we have beautiful fresh snow about 6 or 8 inches.

Vincent: Whoa! Nice.

Michele: So it is perfect for the holiday season.

Vincent: We don’t have any snow here. Today we have a guest on TWIM, it is a crossover from TWIV, he is here right in the studio in New York City with me, Dickson Despommier.

Dickson: Hello, Vincent.

Vincent: Can you handle the microbes?

Dickson: I can, in fact I’m a bona fide microbe aficionado, I have my degree in that area, so I’m really excited to be here. This is my first visit, I hope it won’t be my last.

Vincent: You said you worked on gnotobiotics, nice, but you got rid of the microbes.

Dickson: (laughs)

Vincent: So how could you be a microbiologist?

Dickson: As it turns out, these were the, the only way they knew that they were germ free was to try to culture out bacteria and you know now that there are plenty of them that you can’t culture so these may not be germ free.

Vincent: You should give back your PhD, that’s what you’re saying.

Dickson: Well, they’ve never asked for it back (laughs)

Vincent: And the post doc was where, remind me?

Dickson: At Rockefeller.

Vincent: And that’s where you learned parasitology?

Dickson: That’s what I learned what I should have been learning at Notre Dame, basically.

Vincent: You went there to do parasitology but you never did.

Dickson: No, no, I did, I stayed working on the worm I was working on.

Vincent: Trichinella.

Dickson: I did. That’s right.

Vincent: And these are ages ago that we are talking about.

Dickson: Ages, these are back in the 60s that we are talking about, the 60s.

Vincent: Well, welcome to TWIM and hopefully you enjoy, as I say you always know what questions to ask.

Dickson: (laughs) It’s always the naive “I don’t know” questions.

Michele: Uh oh, better be on our toes (laughs)

Vincent: We’ll be on our toes. Michele, you never ran into Dickson while you were here, did you?

Michele: I don’t believe so, let me try to remember the years I was there. 86, the year of the World Series.

Dickson: There you go, there you go! Now you’re talking. Really, I’m a big fan. I’ve been here since 1971.

Michele: Yeah, I think I left in 86, so I think I came to Columbia when Sam Silverstein moved his lab up from Rockefeller in 84.

Dickson: Yep, I knew him. I was a post-doc at Rockefeller for 3 years, I knew Sam there, too.

Michele: Wow, so that is when I started. I joined the lab in 82 and I was a technician there and then moved with him and worked for another year and a half.

Dickson: You were at Rockefeller?

Michele: I was.

Dickson: We may have met there.

Michele: It’s possible.

Dickson: I mean, I used to go back all the time, I was in the Duves group, so I used to go with Nicholas Muir a lot and talk with him.

Michele: I see.

Vincent: You must have met the faculty club.


Michele: Playing pool, yeah.

Dickson: Drinking beer.

Michele: I really have Sam Silverstein to thank for launching me on a career in science.

Dickson: Cool, I just saw him recently on the street.

Michele: Yeah, how is he doing?

Dickson: I said hello, he’s a little bent over.

Michele: He’s had a number of replacements, joint replacements.

Dickson: Indeed. The last time I heard he had some bad news was when he tried to resummit Mt. Elbrus.

Michele: I know, can you believe that?

Dickson: He just got halfway up and couldn’t make it.

Vincent: I had lunch with Sam Silverstein recently and afterwards he said come here, can you just sit with me for five minutes? And you know that’s an hour.

Michele: (laughs)

Dickson: Yeah, exactly. So you must have known Hersh as well, then.

Michele: Not well, but certainly the name.

Vincent: I thought Dickson was looking lonely out in his outer office.

Dickson: Yeah, you know.

Vincent: So I invited him to join us.

Dickson: There was enough of a quorum sensing molecule to drag me in.

Michael: Oh, no. We’re going to have that kind of TWIM.

Vincent: Dickson’s pretty bad with the…

Dickson: My degree is in microbiology. You get this, I got it at Notre Dame working on germ free animals. (laughs)

Michael: That’s where a lot of the pioneering work on gnotobiotics came out of.

Dickson: Exactly. So I consider myself an amicrobiologist.

Vincent: We are going to give away a book today, and I am not going to tell you about it until later. That might stimulate some email, there’s been a dearth of email on TWIM lately. Maybe this book will stimulate it, but before that you have to listen to a snippet and a paper and we will start with Michael with really a very cool snippet.

Michael: This one is in honor of the location I was yesterday, I was actually in Wisconsin yesterday, America’s dairyland, and the papers that we are going to have as a snippet today is “The nasal microbiota of dairy farmers is more complex than the oral microbiota and reflects occupational exposure and provides competition for staphylococci.” And the paper is by Sanjay Shukla, Zhan Ye, Scott Sandberg, Iris Reyes, Thomas Fritsche, and Matthew Kiefer. And they are all located at the Marshfield Clinic Research Institute which is located in Marshfield, Wisconsin, and Dr. Kiefer has recently moved to the VA Puget Sound or he may have always been in the VA Puget Sound, and so since we are missing Elio, I am going to start the way he often does.

Here’s the story. Many of you know that allergic and autoimmune diseases have been attributed to the lack of exposure to biodiversity, and for those of you who have been following us for some time this is an old variant or chestnut of the hygiene hypothesis that was proposed back before there even was the word microbiome in 1989, and the hygiene hypothesis is pretty straightforward. It proposes that the lack of an early childhood exposure to infectious agents or symbiotic microbes such as the gut flora or probiotics and in honor of Dickson, parasites, increases susceptibility to allergic–

Dickson: I want to clarify that I am not a parasite, thank you. (laughs) Although I have been characterized that way.

Michele: You’ve been called worse.

Dickson: I have been called worse.

Michael: It’s your passion, it’s your passion. And increases susceptibility to allergic diseases by suppressing the natural development of the immune system. And it has also been bandied around in the literature as the biome depletion theory and the lost friends theory. So here the authors are proposing that the microbiome of healthy dairy farmers would be richer in biodiversity than the microbiome of non farmers living in urban settings, principally due to the greater exposure to the microbes that they encounter through their everyday life of milking cows and mucking out the barn and cleaning everything up.

So they are exposed to quite a few microbes and up to this point in time there have not been studies asking this principal question, namely does your profession actually help predetermine what you are going to be colonized with? Some of you may recall from our discussions of Jack Gilbert’s work from the Department of Surgery at the University of Chicago that if you live with a dog or a cat your microbiome will actually reflect that you do indeed have a pet in your home.

But here Shukla and colleagues want to investigate this relationship between the microbiota of dairy farmers contrasted against urban non-farmers. And so they address their question, as you might guess, they compared the nasal and oral microbiota of dairy farmers against the microbiota principally the nasal and oral of urban individuals from the same area. And it is important that they use the same area because of all the demographics and what they principally learned is that the nasal flora of dairy farmers showed a significantly higher microbial diversity with hundreds of unique genera that suggested to the authors that environmental/occupational exposure was indeed significant in determining what was going to live in your nose.

And the nasal and oral microbiomes clustered separately from each other using the standard principal component analysis and they found that the dairy farmer harbored two fold greater complexity in their nasal flora and 1.5 fold greater exclusive genera in their mouth when they compared it to the non farmer. Interestingly, the nasal community of the dairy farmer group had a much lower burden of staph species, again suggesting the correlation between higher microbial diversity and competition for colonization by the staphylococci. And so as you begin to think about this paper, just by reading the abstract, you say, well, this sort of all makes sense.

But the reason I picked this paper is one of the individuals that I have been working on in one of the COMS, the council of microbial sciences, which is an advisory body to the board of directors of the American Society for Microbiology, he sent me an email asking about staphylococci in farmers and wanted to know about livestock exposure, so when I began to investigate his question I stumbled into this paper and I thought it would be a really neat snippet to introduce this new group and to reacquaint our audience with the hygiene hypothesis and really begin to look at the complexity of the nasal flora of humans and contrast it against the oral community. It was really pretty interesting and this group also did indeed query whether or not the scary MecA gene was present in the community of microbes in the nares of dairy farmers. And fortunately it was absent, and so that is good news for dairy farmers and in fact it wasn’t all that significant in the non farmers as well. It was a really fascinating treatise on how they approach this problem.

As I said, what they did is they principally used the V4 region, so this is not total genome sequencing, this is 16S ribosomal RNA sequencing using the V4 region of the 16S ribosomal RNA gene, and they went after 21 different dairy farmers aged 20 to 64 and they had an equivalent number of non farmers from an urban setting. Demographically there was no remarkable difference for them. What always blows my mind having grown up in an era of Sanger sequencing is how many sequences it now takes to make some of these remarkable conclusions that these authors came up with. They looked at 10 million sequences from 78 clinical samples and when you pare that down they had 118,000 reads and you are going my goodness there is so much work going on here, and–

Michele: So much life in the noses of those farmers and non farmers.

Michael: That’s what was remarkable, and one of the things that I like reading the straightforward papers that have an obvious conclusion up front is their obvious conclusion up front was dairy farmers did indeed have a more complex nasal community and a more complex oral community, but what they introduced me to is a term I hadn’t recalled and this was something called the Chao richness factor, and I put into the show notes a PDF the author Chao put into her page and it is freely available to individuals for review. And it really describes the statistics of how you can determine species richness using a sample size of 21 farmers and a thereabout equivalent number of non farmers, and it gives you the base statistics behind estimation and comparison, and what is really remarkable about the was Shukla and colleagues presented their data is the beautiful figures that they showed. They have rick color figures showing the major phyla between the two groups and you start off with that first figure of just looking at this box plot of a Chaow 1 richness.

And when you look at it they had 4 groups in their study. They had the nasal community of a dairy farmer, they had the oral community of a dairy farmer, and similarly they had the same 2 groups of the non farmers. You don’t need an advanced degree in statistics to notice in that first box plot the nose of the dairy farmers was significantly different than the other three groups. It really sets the tone of what is actually going on. The nasal microbiome of the dairy farmers was indeed richer and more diverse.

And as Michele tumbled into, it was extremely diverse in terms of the number of organisms that were present and when you begin to look at the organisms that are there, many of them are old friends of those of you who are familiar with the major families that live in the oral cavity, namely the firmicutes, the actinobacteria, the firmicutes recall are the garden variety gram positives, the clostridia, the bacillus, the staph, the strep. The actinobacteria include the gram negatives like homophilis, eikenella, the proteobacter of course are your friends E. coli, they also had the bacteroideadeas, which are bacteroides and other gram negatives. Of course the stinky bacteria, namely the fusobacteria species, that are there. And these were the principal families that were coming out of this group, and when they compared and contrast the nasal community it had significantly higher numbers of these bacteroides and actinobacteria in the nasal samples compared to the oral bacteria, and in fact they had hundreds of exclusive genera that were present in the nares of the dairy farmers. In fact, they had 2 times more genera, they had 1,189 unique genera versus the 552 genera that were present in the nasal flora of the non farmer. And that of course was significantly different.

Michele: Michael, could I jump in?

Michael: Please interrupt.

Michele: In addition to those box plots with the whiskers and all and the statistics, I also appreciated that in figure 5 they included a classic Venn diagram that allows us to just glance pretty quickly and appreciate that the nasal passages of the dairy farmers did have quite a lot of overlap with the non farmers but they had what some 431 different phyla that were unique to the dairy farmer and not seen in the control populations. It’s just a very easy way to grasp those population distinctions.

Vincent: It’s very nice.

Michele: I also just want to emphasize that these dairy farmers have a richer diversity and rich really is the right word here because in the literature with microbiomes we are seeing again and again that the more diverse population you have on your body, on your surfaces, that correlates with better outcomes, more health. So just to make sure our audience understands that the increased number of different types of bacteria in the nose of the dairy farmers is a good sign, although they did not do that analysis here.

Michael: No, and in fact I think there is a lot that one can take from this paper in terms of thinking about things. Elio in our early discussions of the microbiome when we were reporting sequencing talked about well, you’re developing a New York City telephone directory with millions of entries. So what does it mean? They began to do that richness analysis and this was where I was going to introduce the Venn diagram figure 5 where they begin to talk about the common genera. So there were 503 common genera or 28.9% which I then coin the term is this the core microbiome of the nose? Like we have a core genome of an organism, is this the core microbiome of the nose? And when you can’t contrast that to the core oral organisms that were common between the non farmers and the farmers, that was 28.6%.

So it leads to me channeling Elio’s thoughts about, so what that you’ve got all these different bacteria, but what does it really mean? You looked at this core microbiome of the nose. There were 503 unique common genera and similarly in the oral cavity there were 28.6 or 279 organisms common to the oral samples. You know, but the nasal samples from the dairy farmer had 431 exclusive genera and they have a nice table where they compare and contrast the microbes in the farmer versus the microbes in the non farmer and since this is a snippet and we don’t have much time to get into it I will leave that for the audience to review the compare and contrast, because I think it is important that as you read this paper, and again this is one of the PLOS papers, so it is in the public domain so you have ready access to see the figures and see the paper, in fact when you look at the top 5 relatively abundant nares species from the dairy farmers you see that about 20% were crynibacteria, the staphylococci only about 9.4 percent then they have a gram negative moroxella at 8.1% an organism I had never heard of, dolosigranulum was at 7% and streptococci were down at 3.3%. Contrasting that to the non farmer, the staphylococci are high at 34.6 but interestingly the crynis are very similar in percentage, 19.7 in the farmer versus 19.9 in the non farmer and again the common species of moroxella in the farmer was 8.1, the non farmer was 8.5 but instead of having that unusual organism dolosigranulum, they had pseudomonas.

Michele: Right, I thought that was interesting.

Michael: Pseudomonas is this organism, a soil organism, so I would have expected that more in the farmer where they have hay and the cows are bringing in dirt from the fields. But it was remarkably absent from the farmer in the sense it didn’t make the top five percent. And then you had peptinophilius, again an organism I am not familiar with, and it was at 5 percent so it obviously must be going after a peptide given its name. But it was interesting looking at what was going on there and what was remarkable was when they contrasted it to the oral flora, the oral flora really wasn’t any different between the two groups. The oral flora of the farmer was effectively not significantly different from the oral flora of the non farmer, and that may be due to the diet that we all have in common and the oral cavity is a portal of entry for that particular occasion of coming on in.

Michele: Michael, I liked your thought about this type of approach to identify for the first time the core genera I guess we would have to say of the nasopharynx but in this particular case because they looked at such a small population, 21 farmers from two different farms in one area of Wisconsin, and they sampled only on one day in June, I think this is the first contribution to that effort but they will need to do additional populations and also I would guess different seasons. I’m guessing what we have in our nose in June is probably different from what we have in say, late December.

Michael: Yes, it is much drier here and so I think the crynibacteria will actually win out. In fact, that is one of the limitations of their study as you brought out. And that was what I was going to bring up just before you did, is the limitation of studies like this is it is driven by the size of the species and again this is just one of the first, it is a unique community dairy farmers are unique, and they point out in their discussion that they specifically targeted dairy farmers over other types of farmers, such as grain farmers or farmers growing crops that, truck farm types that are growing crops that go into what we would assume the farmers market things like tomatoes and cucumbers and squash and watermelon and all the things that we seasonally are in delight when you go to the farmer’s market throughout the summer.

So this is but phase 1 and in summary, keeping to our time of making a snippet, to tease the audience to go and look at this in great detail, the authors did conclude that dairy farmers do indeed have a rich microbial community significantly richer than non farmers. The oral cavity between the two groups wasn’t statistically or significantly different than one another and hey are encouraging us to think about the hygiene hypothesis or the microbial friends theory that as you are exposed to these things it may lessen the likelihood of autoimmune type occurrences like asthma and allergies that we commonly associate with, and that is of course where the hygiene hypothesis came from, is asthma and of course hay fever. So I commend this paper for you all to take a look at, it is a great paper from looking at it from the perspective of how to present complex data sets that you can easily digest. I would encourage you to look if you spend any time on the paper, look carefully at figure 5 because it really shows you the power of a Venn diagram in figuring out what is remarkable when you begin to compare and contrast these things, and I think as Michele pointed out we are going to need many more communities of farmers included in this, Wisconsin is but one, we all know where happy cows are, they are out in California, and so as the nasal flora of a dairy farmer in Wisconsin where yesterday was -9 below, and it doesn’t get that cold in California where the happy cows are.

Dickson: Except the ones that are caught in the fires.

Michele: Right.

Michael: Except the ones that are caught in the fires. So we want to take a look at it and it is a really neat study and it didn’t get at Tyler’s question, Tyler Rathe is the one who asked me the question about what is going on with if there is any correlation with farm staphylococci entering the clinical community and this was the first study showing that the nasal microbiota of dairy farmers is different than non farmers.

Vincent: So if one of these farmers went to the city for 6 months, would the nasal microbiome change completely?

Michael: I don’t know.

Michele: Good question. Or would it be stable?

Vincent: You would imagine that, well, some people are going to be born and raised and lived their whole lives on a dairy farm, right? So is their microbiome stable even if they leave, right? Are the health benefits going to stay with them or are there health benefits? We don’t know.

Michele: Is your immune system already imprinted for that reexposure?

Dickson: So somebody here who is in South Carolina, they don’t have a lot of dairy farms in South Carolina, but they have a lot of pig farms.

Michael: They do indeed.

Dickson: The parasite I worked on all my life, trichinosis, is associated with that particular animal, so I would wonder how this plays out in regards to two things. One is that I want to know whether or not farmers have fewer allergies. It seems to me that they have as much hay fever as most other people, but I don’t know that for sure. The kinds of cows that are raised for dairy farming, they are not all the same, so it would be very interesting to see how this varies with the cow type and thirdly, of course, is to see whether it has any clinical correlations with any of these hypothesis.

Michael: And they point that out about the species of cow that they were looking at and as Michele pointed out this was from two farms, but they already had 10 million sequences in the bank.

Dickson: That is incredible.

Michael: It is a lot of work and the question is you begin to push it forward and how many studies do you need to conduct in order to begin to determine these sorts of experiments that need to be done next? I think that is where the big data community begins to come after us, because as we all know as this was the season of big data, if you made the mistake of shopping on Amazon or any of these other online websites and you accidentally clicked on a coat or clicked on a pair of shoes, what you saw on your internet browser for the next four days was that same coat or that same pair of shoes.

Vincent: Yep, you bet.

Michael: And so that is what I think we need to begin to bring to the science of the microbiome is to begin to incorporate all of these data sets together in a similar manner that Facebook and Amazon does to begin to understand shopping trends and what not and so you could well imagine that one of the unique species of the nose of the dirty farmer could be that coat or that pair of shoes that you were looking at when shopping on Amazon and if you get another dairy farmer looking at something else or a farmer or an individual in the city should you suggest that coat or all of those things, and I think we are at the beginning. So that is why I put into the show notes these two little guides on species richness estimation and some of the underlying statistical theory behind how these studies are beginning to be assembled.

Dickson: Thoughts creep into everybody’s mind when you listen to all of this for the first time and of course the group that I would really love to see some of these studies done on is a large animal and a small animal vet.

Michael: Oooh.

Michele: Oh, yeah.

Dickson: There are tons of veterinarians and they get their hands way inside these animals.

Vincent: Yeah.

Michael: Oh, yeah.

Michele: And they would be willing participants in this.

Dickson: They sure would be, they would be.

Michele: That’s a great idea. So before we move on I want to give a shout out to Marshfield, Wisconsin so this study was done by a group at the Marshfield Clinic Research Institute and Marshfield is a town of about 20,000 people midway between Green Bay and Minneapolis. By looking at the World Wide Web I learned that they are highly ranked by a number of studies for their quality of life. They are proud to be considered one of the best places to live in Wisconsin. They have a couple of health care facilities that they are proud of and parks and a great way of life, so I want to thank the about 40 citizens from that area for contributing to this study.

Vincent: I learned that 33% of dairy farmers take less than 1 shower per day.

Michael: Yeah, I didn’t bring up all of the demographics because it was extensive.

Dickson: How many of those live alone? (laughs)

Michele: Yeah, I was going to say, those would be the bachelor farmers.

Vincent: By contrast, only 6% of non farmers take less than a shower a day, because they have to work, they have to be around other people, so that was really interesting.

Michele: Maybe they are taking baths.


Michael: Their demographic study has how many have household pets, whether they have a dog, a cat, a horse, a rodent, a rabbit.

Vincent: Fish. Birds. Yeah, that’s pretty fun.

Michael: So their demographic table really gives you how much work this group indeed put into this fine study. It is an interesting snippet, it is easy to get through, the statistics are approachable if you use the resources. It is a good snippet.

Vincent: Thank you, Michael. That is cool.

Michael: Thank you!

Vincent: Our paper was suggested by listener Hannah who wrote back in May, my lab’s journal club is doing this paper today and I thought it would be a good fit for TWIM or maybe even TWiEVO. It is about insect endosymbionts that regulate their own virulence through quorum sensing. Basically at the beginning of the infection the bacteria produce a lot of toxins when they sense that they have colonized thanks to quorum sensing molecules they suppress all those virulence factors. This allows them to establish a persistent infection without further injuring the host. All of this has implications for how mutualistic relationships with microbes can arise, which I think is pretty cool. So the paper was published in Cell Host and Microbe, it is called “Quorum sensing attenuates virulence in Sodalis praecaptivus.” The authors are Shinichiro Enomoto, Abhishek Chari, Adam Clayton, and Colin Dale, and they are all from the University of Utah, the department of biology.

Now on TWIM we have talked multiple times about endosymbionts of eukaryotes, bacteria that live within eukaryotes, and there are only certain phyla of bacteria that are predisposed to enter this kind of mutualisms. One of them is the Sodalis genera, of course wolbachia, another one, and really why this is limited is an interesting question. These endosymbionts often provide metabolites like amino acids, vitamins, and they can be used, they can be made by a wide variety of bacteria so that doesn’t explain why certain phyla would become endosymbionts. Maybe it is the genetic adaptability of the bacteria that is involved. They discuss a bit this problem of virulence when a bacteria enters a eukaryotic cell it tends to be virulent which of course might end up killing the cell and so to become a mutualist you have to suppress that and that is going to allow the bacteria to live inside the eukaryote. And that is one of the things they investigate here and their system involves this insect endosymbiont Sodalis praecaptivus which usually is inside a grain weevil host and it is related to other similar Sodalis endosymbionts. One of them is an endosymbiont of the tsetse fly which is Sodalis glossinidius. Dickson must know very well, you know the tsetse fly very well.

Dickson: It rolls right off my tongue, my oral cavity I might say.

Vincent: So that is an actual mutualist that one, and that is why this comparison is interesting between Sodalis praecaptivus and the others because Sodalis praecaptivus is not yet a mutualist, it comes and goes within the eukaryotes, they have to be reacquired all the time by horizontal transfer where as the mutualists are vertically transmitted from mother to offspring and these eukaryotes, the weevils, the tsetse flies have to live with them their entire lives, whereas the Sodalis praecaptivus is interesting because they are reacquired, they are not maternally transmitted and so it is a transient association.

So you may ask why would a bacterium have a transient association with a bug of some kind? And we don’t know the answer but they suggest that it may be an intermediate vector to transmit it to another host. Stinkbugs for example feed on trees, so they said maybe the stinkbug is giving it to the tree and that is the function of it. So the point here is that Sodalis praecaptivus is a nice model because it may be an intermediate so these related Sodalis species all arose from a common ancestor and some of them are mutualists and some of them are not so maybe you could learn something about what it takes to be a mutualist or to become a mutualist by studying the ones that are not yet.

Michele: And Vincent, I’ve just learned that the word sodalis is latin and it means companion, fellow, intimate, accomplice.

Vincent: Perfect, right.

Dickson: Filidarity.

Michele: So it reinforces that.

Vincent: Yeah, that’s right, filidarity. Filidarity with sodalis, yes. So in this paper, what they do, they use Sodalis praecaptivus to study what it takes to become a mutualist. Remember, Sodalis praecaptivus is not yet a mutualist. And what they focus on is quorum sensing as a way of achieving mutualism. This of course is a system where bacteria make pheromone that increases as the bacterial density increases and past a certain threshold concentration it interacts with regulators in the bacterium and it changes gene expression. So a really well known effect is the ability to make bacteria glow with the production of luciferaces and that happens only at a certain density of bacteria which is regulated by these quorum sensing molecules.

So they want to know if quorum sensing in Sodalis praecaptivus is involved in somehow regulating its interaction with the host. So the first experiment they did was simply to ask, does praecaptivus make a quorum sensing molecule? And glossinidius, which is the sodalis from tsetse flies, is known to make a quorum sensing molecule which is called 3-oxo-hexanoyl homoserine lactone which we will abbreviate OHHL. That is the molecule that is produced and which communicates within the bacterial community. And they have a cool assay, they take an extract of the praecaptivus, they fractionate it by thin layer chromatography, and then they take the sheet which they have used to separate the extracts of the bacteria and then they overlay it with another bacterium that has a reporter in it which will produce a blue spot when there is the homoserine lactone present. Isn’t that cool?

Michele: That’s very cool.

Vincent: You don’t have to do any mass spectrometry.

Dickson: Bacto blot.

Vincent: Bacto blot, yeah. So by this they can tell that praecaptivus makes an OHHL and that is important for the rest of the paper. So OHHL is synthesized by an enzyme encoded by the YPE1 gene and they can see by looking at the genome of these sodalis that they have this gene, and there areas of genes involved in the response to the lactone. That is known and they can compare the genomes of praecaptivus and glossinidius and see that there are 2 genes called YPER and YENR and these are response elements, they are important for the response to the lactone. All of these are going to come up as important players, I know it is hard to remember them but just remember the lactone which is the quorum sensing molecule is produced by one gene, YPE1, and then there are two other different genes involved in the response to it.

Michael: And so Vincent this is really the classic gram negative quorum sensing circuitry that some of our listeners may be familiar with on the quorum sensing molecule is made, it is thrown out into the medium for free for all other microbes to investigate, and then it freely diffuses back into the responding organism and that homoserine lactone moiety then serves as a positive activator to activate transcription in the respondent bacterium of a particular behavior. So that is in contrast to the gram positive quorum sensing system that uses a peptide. So this is the canonical gram negative quorum sensing circuitry that many of you may have been familiar with. It is found in many of the common textbooks because as Vincent said it was the one that gave us light.

Vincent: So the typical homoserine lactone effect in vibrio is to make light, and that interacts with the luxR response elements to turn on the production of luciferase and then the squid which bear the vibrio will then glow at night so they are not eaten by predators swimming below them. So here in the genome of this sodalis they can see LuxR like response genes and those are the YPER and YENR genes, and those are genes that will respond to the homoserine lactone and have whatever the biological effects are in this particular bacterium.

So to go through just a few of the experiments they did, first they want to know what genes in praecaptivus are regulated by this homoserine lactone and they simply treat bacteria in culture, they take bacteria lacking the synthetic gene for the homoserine lactone, so you have no activity, they add homoserine lactone and then they ask what RNAs are turned on or turned off. They do transcriptomic analysis and lucky for them 30 genes–

Michele: 30, not 800.

Vincent: Yeah, I mean if this were eukaryotes it would be 800 or 1,000.

Dickson: A veritable plethora.

Vincent: If you wrote a grant to look at them they would say no way.

Dickson: A fishing expedition.

Michele: A fishing expedition.

Michael: A fishing expedition would come in.

Dickson: I’m very good at fishing.

Vincent: But here, there are 30 genes with greater than four fold change and most of them, 26, showed a decrease in expression in response to this homoserine lactone.

Michele: So rather than turning on a light, it turned it off.

Vincent: It turned it off. And these genes that are turned off, they can tell what they do because they look at the protein and there are other proteins in the database that are similar. Their functions are associated with causing diseases in insects like toxins, chitinases which would digest the chitin protective shell of the insect.

Michael: You’d get a very soft roach.

Vincent: (laughs) Digest the insects from within. Collagenases and so forth. So those, keep in mind, we will come back to those. And then four genes went up, and two of these are CPMA and CPMJ. We will come back to them yet. Now, we take a little detour here and go to these LuxR response like genes, YPER and YENR. It turns out that these seem to be transcriptional regulators, they are involved  in the response to homoserine lactone. Exactly what they are doing they are not sure but keep that in mind there is this interaction between the biosynthetic gene that makes the homoserine lactone and there is the other 2 genes that regulate the response to it. Here is the cool part, this is all background so far. They notice, this is where good stuff always begins, we notice during the course of our work–

Michele: During the course of our study–

Dickson: We naturally observed–

Vincent: The wild type strain, so we have two strains of praecaptivus, we have a wild type and one with a deletion of the gene of the biosynthetic gene for this homoserine lactone. They notice that the wild type growth rate was really much less than the mutant which can’t make the homoserine lactone. They  validated that by showing that if you add the homoserine lactone itself to both wild type and mutant strain it will inhibit their growth. The quorum sensing molecule is inhibiting the growth of these bacteria. Of course, remember these two LuxR like responsive genes which I said were transcriptional regulators? If you delete them, then homoserine lactone does not affect the growth of the bacteria. So that makes sense because we know the products of those two genes are involved in the response to the quorum sensing molecule. They do some cool mixing experiments where they mixed wild type and mutant strains and they could show you that it is in fact this quorum sensing molecule that is causing the inhibition of bacterial growth.

So why, what is the gene responsible for growth suppression caused by the homoserine lactone? They made mutants of the praecaptivus and they looked for mutants that relieved the growth suppression caused by the homoserine lactone. They found that CMPA is a major gene involved in growth suppression caused by homoserine lactone. And you may remember but you won’t so I will remind you that CMP was one of four genes that went up when you treated cells with the homoserine lactone. So exactly what it is doing they are not sure but it is clearly responsible for relieving growth suppresion caused by the presence of homoserine lactone. So then the next experiment is to take weevils, these are adult grain weevils, they treat them with antibiotics to reduce their own native symbionts, and then they inject praecaptivus into them. The can inject wild type or they can inject a mutant that cannot make quorum sensing molecules. So what do you think happens? They look at these injected weevils at one week, the ones that got the strain lacking the ability to make the quorum sensing molecule, they started to get lethargic and then they died over the next two weeks.

Dickson: They became the lesser of two weevils.

Vincent: (laughs) The lesser of two weevils, very good.

Michele: (laughs)

Michael: That could be the title.

Vincent: And the wild type injected weevils were fine.

Dickson: Great.

Michele: That must have been a great period in the lab to start collecting this data.

Dickson: That’s a Louis Pasteur response, it comes back the next morning, he claps his hands and only half of the sheep wake up.

Vincent: I don’t know that story.

Dickson: It’s from the vaccination of sheep against…

Vincent: Rabies?

Dickson: Yes, that’s correct.

Vincent: So he clapped.

Dickson: He clapped and they were all asleep, he thought they were all dead. Only half of them were.

Vincent: And those were the vaccinated ones?

Dickson: That’s correct.

Vincent: Good story. If you are wild type for the biosynthetic gene for this quorum sensing molecule you are fine, but if you take out the quorum sensing gene, you die.

Dickson: So not only does it slow the rate of growth down, or division, cycling?

Vincent: We don’t know exactly but they are not–

Michele: They don’t say. And they don’t say whether they are killing or if it is a growth inhibition, if you wash away the quorum sensing do they rejuvenate? Does it say?

Dickson: Do we know that this approach has identified any new toxins that might be useful for insect control?

Vincent: They do identify some toxins, I don’t think they are new, though. But they have some other things that are involved, I will get to that in a minute. So now, they take this cool experiment and they make double mutants where they combined the biosynthetic gene that encodes the enzyme that produces the quorum sensing molecule along with the deletion in one of these two regulatory responsive genes. In fact if you combine the two responsive elements, if you mutate both of those together that will kill as effectively as a deletion of the biosynthetic gene. And here in fact, I misspoke earlier, here they do the mixture of wild type and mutant strains. If they mix a wild type bacteria with the biosynthetic mutant which kills the weevils, the wild type will suppress the killing, so it is obviously making a secreted substance, right? But if you mix wild type bacteria with bacteria mutated in the response element, the wild type will not mitigate the killing of them because they can’t respond, because the YPER and the YNER are responsive elements for the quorum sensing element.

Michele: Those are beautiful experiments.

Vincent: Yeah. So this is great because you have an animal model, an insect model, you can manipulate the bacterium and know exactly what is going on. So you can say okay, this quorum sensing molecule is somehow protecting the strains.

Michele: And you feel like a genius (laughs)

Dickson: What kind of medium do they use to grow these things in vitro?

Vincent: I would have to look it up, I don’t know.

Dickson: Okay, just standard microbial medium.

Vincent: To grow the bacteria?

Dickson: Yeah.

Vincent: We can look it up very quickly, here, let’s see. Of course the materials and methods are not in the PDF. Hold it, here we go. They are grown on organic whole yellow maize, by the way.

Dickson: (laughs)

Vincent: (laughs) And the symbiont free weevils which are generated by treating with rifampicin, but let’s get to the bacteria. Here we go. Bacteria were grown in LB. There you go.

Michael: A lousy medium.

Vincent: Just the standard LB.

Dickson: So the insect doesn’t contribute anything to the bacteria’s ability to reproduce?

Vincent: The bacteria can be grown.

Dickson: Of course, but in the symbionts–

Vincent: That’s a good point. These captivus have not lost genes that they need to grow on their own because they are not endosymbionts they are just transient partners in this association.

Michele: So they are more versatile metabolically.

Vincent: Exactly. But the one in tsetse flies, they have undergone genome reduction, they have lost genes so they may not be able to grow on their own. They are stuck inside the fly.

Michele: They are feeding off free nutrients.

Vincent: So now we know that the quorum sensing molecule is involved in weevil killing, so what gene is involved? They can do another screen that can look at some of these genes that were differentially expressed that they looked at early in the work and ask if you combine, if you knock them out in a weevil in a bacterium, I keep confusing the weevils and the bacterium, if you knock them out in a bacterium that lacks the ability to synthesize the quorum sensing molecule and you inject those into weevils and you see which suppresses the killing, none of the double mutants were completely relieved of their ability to kill weevils but they were some that were significantly suppressed, and in fact a gene called RegC which turns out to be a transcriptional factor, so it probably regulates some of the genes that are involved in the killing so we don’t know what is going on there.

But combining the biosynthetic gene with these two genes called PEERA and PEERB, these two genes encode toxins that are probably lethal for the insect. That combination delays the killing. And PEERA and PEERB are a binary toxin complex and so you need both of these for killing activity. That is probably one main way that the killing is progressing. And of course they think there are other killers that they have not identified yet, as well. And finally at the last experiment they deleted this gene CPMA. Now you remember that there are actually two genes, A and J, CPMA and J were the original ones observed to go up when you add the quorum sensing molecule. They are involved in growth suppression so if you add the quorum sensing molecule to these bacteria it suppresses the growth and CPM A and J are involved in that.

So they made a double mutant of CPMA and J, they inject that into the weevil, it doesn’t grow very well. So what does all this mean? We could put most of this together. So we have a bacterium praecaptivus it enters the weevil at some point in life and to enter and begin to replicate it has to express factors like toxins chitinases, and those enable it to grow.

Michele: Probably to get access, right? It has to break down some insect barriers.

Vincent: Right. So these are the things that are killing but early on the growth of the bacterium inside this weevil, of course they don’t want to kill it but they made it low enough amounts so that the bacterium can enter, as Michele says.

Michele: Slip in.

Vincent: And then when the bacteria have reached certain numbers they are producing these quorum sensing molecules which then shut off the production of these toxins so they are not going to kill the insect. And we know that CPM AJ are involved in this shut off, you can’t delete that, if you delete those you can’t even infect. CPM A and J are involved in the production of these toxins in response to the quorum sensing molecules and if you delete CPM A and J the bacteria can’t really get established so they don’t really grow very well. So then you get lots of bacteria growing, you get the quorum sensing molecules, the toxins are shut off and then you have a nice coexistence of the bacterium with the weevil for as long as you need. So this bacterium has learned how to modulate virulence.

Dickson: When they are inside the weevil and they have done that, where are they found? Are they found on the hemocoel or are they found within cells?

Vincent: These are intracellular.

Dickson: Which cells?

Vincent: I don’t know. They actually don’t mention that but I am sure there is an extensive background on this.

Dickson: It would be wonderful to see which cells are the repository.

Vincent: Why would it make a difference or be important?

Dickson: I think that if you had a transitional organism, like we have in parasitology for instance, strongyloides is a parasite that can reproduce in the soil by just eating bacteria or it is an obligate parasite inside of a mammalian host. So you have these two pathways that you can go to. Wolbachia never comes out of the cell. Whereas this presumable developmental endosymbiont enters the weevil as a parasite and then modifies its behavior to become more friendly, as you put it. And then which cells are the beneficiary of this relationship?

Michele: And it would give you clues about transmission to the next plants.

Dickson: It would.

Vincent: That’s right. I don’t know how transmission occurs but maybe they are shedding it.

Dickson: I presume the chitinase is totally shut down, right?

Vincent: Yeah, the chitinase is in the protein toxins, they all have to be shut down, otherwise it would kill. If we mess with the shutting down we kill the adults. Now the tsetse fly version of this bacterium, glossinidius, they don’t have these quorum sensing regulated virulence genes, they don’t have the protein toxin, they don’t have the chitinases. They don’t need it because they don’t have to enter. They are given to new tsetse flies at birth. So they don’t need any virulence factors.

Dickson: It’s vertical.

Vincent: So that’s the idea emerging out of this paper, which I think is cool. You have a bacterium which is entering a host and to do so it has to express some virulence genes to get in but then they are suppressed to allow the host and the bacterium to survive. Eventually, over time, if you wanted to make that a true mutualism you don’t need any of this quorum sensing business anymore. You would switch to vertical transmission and you don’t need any of this.

Dickson: It sounds like bacteria thinking about doing this.

Michele: (laughs)

Vincent: I don’t mean to do that at all but it is obviously easier to describe.

Dickson: I know, I know, I know. They are selected for life by their metabolic price tag. So there is a metabolic price to pay for making more genes.

Vincent: For sure. So they have a nice discussion where I really like the evolution of virulence, in viruses we think about it all the time. But here, if you have a bacterium that is evolving towards mutualism, you have to reduce virulence. In this case we have a nice way of regulating it during an infection but eventually you would lose the genes that accomplish virulence. And then you go from horizontal to vertical transmission. So here this particular praecaptivus is still being transmitted horizontally, but presumably at some point you would go vertical, and at that point what happens, what are the conditions? That is really interesting.

Michele: Again, it probably depends on what cells they have access to. Whether they can be maintained in the germ line.

Dickson: Exactly.

Michael: And the concentration of the homoserine lactone, and that goes back to Dickson’s question about where the microbe is because it is how that homoserine lactone is going to get diluted. Remember, the microbe is giving it freely to the environment and depending on where that homoserine lactone goes, and those of you that remember your chemistry recall that homoserine lactone moiety is not all that stable and it is easily degraded by endogenous enzymes. So my suspicion is that this praecaptivus is actually playing both ends, it is playing this concentration game because it is to its advantage, and Dickson I think may have tumbled to it. It is the compartment that the microbe is in and that homoserine is enabling it to have that selective advantage so it downregulates itself so it continues to feed and reproduce until it needs to go away and it is all about that quorum of how many of the praecaptivus are there as to determining this whole virulence cascade that we are witnessing.

Vincent: It is a cool system for studying this, the experimental details aside, it is kind of an intermediate in the progression to mutualism, that’s why it is neat to study.

Michele: I loved the discussion as you pointed out, Vincent, it really got me thinking about evolution of virulence factors having to overcome host barriers. And then in thinking about the paper that Michael did, and our appreciation for all the good our microbiome provides us, do you think there is a new frontier in science where host cells are actually gonna put out the welcome mat for microbes to try to encourage beneficial microbes to come and stay?

Dickson: If Lynn Margulis was alive today, I would love to hear her answer to that question.

Michele: (laughs) Because we love to talk about the fact that microbes outnumber our cells by maybe an order of magnitude and all the benefits that we get from them, so is it naive to think that the host has only defense systems and not welcome mats, like come on in?

Vincent: That is a good question, we have defense systems and the question is do these bacteria that colonize us, do they overcome them or do we lower the guard to let them in to a certain point? I recall a talk by Laura Hooper from southwestern and she said that the very thin layer above your epithelial cells in the gut–

Michele: The mucus.

Vincent: That is where–

Michael: It’s that war.

Dickson: It’s where the rubber hits the road.

Vincent: That’s where this fight is going on, and I can’t remember the details now but you can imagine that defenses might be lowered in certain areas to allow for colonization.

Dickson: Let’s hear it for secretory IGA.

Vincent: That’s an interesting question, and I think that systems like this will help to understand what is going on there. That is pretty cool. All right. This is from the University of Utah, so if any of the authors are listening, answer our questions about where these bacteria are and so forth. If not, my cohost Nels Elde of TWIEVO is at Utah, he probably could.

Dickson: Another intriguing thought here that is triggered by this whole thing is that these two life forms have been around for a very long time.

Vincent: Which two?

Dickson: The microbes and the insects. They have had plenty of opportunity to develop every kind of relationship possible that you can imagine. And many of them are trapped in amber. So I wonder if you could look back and see…

Michele: Into the genomes?

Dickson: Yeah. I know a lot of the DNA is destroyed in the process of embalming in that material but you can also isolate a lot of material from it as well. You can’t recreate a dinosaur but you could certainly get some hints, because weevils are a very old order of insects. They existed for a very long time.

Vincent: I think the ancient amber is not going to have any DNA in it.

Dickson: No, no more DNA, but maybe some hints at endosymbiosis if you could just cut across there.

Vincent: But you can’t make dinosaurs from it. Not gonna work.

Dickson: Sorry, kids. Can’t have a mammoth for Christmas.

Vincent: Thanks, and right. We have just a couple emails here, let me read them. One is from Josh:

Hello Vincent!

I have been enjoying your show for several years now. I think your show’s conversational style and exploration of topics allows for people of all backgrounds to enjoy complex topics related to biology. Every one of your hosts in the TWIM/V/P has a knack for presenting material very clearly and your passion and excitement for the field is infectious.

Your discussion in TWIM 166 about the PNAS paper “Contemporary H3N2 influenza viruses have a glycosylation site that alters binding of antibodies elicited by egg-adapted vaccine strains” was fascinating. I wanted to see if you had any speculations about why the egg environment might select for this glycosylation site mutation in HA.

I don’t know, that is a great question. So the glycosylation site, is it the tip of the HA and that is where the receptor is interacting? So maybe receptor utilization requires a change at the glycosylation site. What is interesting, Josh, is that apparently the mutation is also selected for in cells in culture, mammalian cells in culture. So it is not just eggs, it is some more general issue. I don’t know what it is but I would suspect it is receptor binding because there is no antibody in the egg or in the cell culture, so the selection has to be independent of antibody. Josh suggests a pic of the week, this is quite the hobby for anyone interested in microbiology or likes pretty things, and this is a compendium of photographs of aquaria and terraria. From all over the world people have sent in their pictures of terrariums, it is very pretty. Check it out, thanks for that, Josh. The next one is from Anthony.

“Raw pet food as a risk factor for shedding of extended-spectrum beta-lactamase-producing Enterobacteriaceae in household cats.”

So this is a PLOS 1 paper which says feeding your cats raw pet food will increase their likelihood of shedding these antibiotic resistant enterobacteria.

Dickson: Sorry, I don’t understand raw pet food. I thought it was all sold raw and eaten raw, but it is processed, no?

Vincent: I don’t know. Not quite sure.

Michael: There is fresh pet out there.

Dickson: But do you have to cook before you serve it?

Michael: No, they sell it in the refrigerated section, you walk into WalMart and you see this refrigerator with what looks like giant sausages and it is FreshPet, ready to go, and it is raw meat that has been homogenized and there have been some fillers added or not depending on which version you buy.

Dickson: Not frozen?

Michael: Not frozen, it’s fresh.

Dickson: Good lord.

Michele: Well I guess tigers didn’t used to cook their food (laughs)

Vincent: That’s right.

Dickson: But polar bears did (laughs)

Vincent: They fed cats this food and then they sampled their fecal material for three weeks and they looked for these particular antibiotic resistant bacteria.

Dickson: I know this is irrelevant to this particular conversation but I actually was hired by a good company, General Foods, to look at Gaines-Burgers–

Vincent: That’s pet food, right?

Dickson: That’s pet food, to look at whether or not it was toxic for trichinella. They wanted to know if they could use pork in their product.

Vincent: I see.

Dickson: They paid me a fairly good side dish so to speak of laboratory funding to look at this and it turned out that they use a preservative and the preservative is ethylene glycol.

Vincent: Wow.

Michael: Oof.

Vincent: In pet food?

Dickson: Yeah. Very small amounts, and believe it or not, that alone killed the trichinella larvae.

Vincent: I was surprised to learn that quite a few people feed their cat raw food exclusively. In addition to the bacteria, there is the public health hazard of toxoplasma. Yes, freezing does kill a high proportion of the bradyzoites. In Russian Roulette, a high proportion of the chambers in the gun cylinders are empty. That does not make it a good idea.


Vincent: How many toxo would you need to infect the cat, though? Because one bullet will kill but maybe one parasite, microbe, virus will not, right?

Dickson: They have done these studies believe it or not in lots of different animal hosts including humans for cryptosporidium as to how many oocysts are necessary to initiate an infection and for cryptosporidium it was around 10. For toxo I think it is less. They are highly infectious. Because of the data that they are collecting from the sea otters off the coast of California because they are dying from toxoplasmosis. They are receiving very low doses to begin with. So I don’t know the answer directly but I think it is known if you look it up.

Vincent: Do you know anything about toxoplasmosa in raw pet food?

Dickson: Depends on the pet food. I mean, if you use lamb, or if you use pork or calf and they are kept on a farm and they are surrounded by cats then chances are 100% almost that they will have got it.

Vincent: Interesting.

Michael: And most farms have cats.

Dickson: They do, because they have mice. (laughs) And that is another story entirely.

Vincent: Our dogs get these little dry pellets, so.

Dickson: Exactly!

Vincent: Another one from Richard:

Hi esteemed professors,

I haven’t written in for a time, having stopped listening for a few years. It wasn’t my choice, but due to a prolonged hospital stay.

Dickson: Oh dear.

Vincent: I’m sorry to hear that, I hope you are getting better.

First the weather here in Bristol uk, is 3 deg C, cloudy, with 5 km/h wind. There is a little snow on the ground that fell this morning.

Regarding cooling towers, a subject I know a little about from my water treatment background, I can fill in some of your questions from twim 165.

Wet cooling towers are indeed a risk for legionella, usually there is a dosing system, that constantly doses biocides into the cooling water. It’s often (in the uk at least) the failure to maintain this, that causes issues, plus as you say resistant bacteria still grow.

In the uk dry cooling towers are preferred, and yes, generally made from copper. These don’t use water, so are less problematic, but less efficient.

Vincent, as you say water towers are closed, and generally drinking water supplies are dosed with chlorine dioxide. The level of chlorine dioxide in the water should sterilise it and prevent any legionella.

Hope that proves informative.

Regards Richard


Thanks for all the work you do, particularly twiv and twim. Though I have a lot of catching up to do, I intend to listen to every episode. I’m slowly working through about 3 years worth while still in hospital.

Now what is a dry cooling tower, does anyone know?

Michael: It is just like your heat pump. It effectively passes the liquid inside the tube and there are a lot of fins that surround the tube and you blow air across it and it dissipates the heat.

Vincent: Instead of using water cascading down the tower like we do here.

Michael: Down the tower, it effectively adds surface area by having those fins and so it is not as efficient but it does the trick. You just have to have a lot of aluminum fins on it. If you have copper fins, of course the heat transfer coefficient is a little bit better.

Vincent: And it will have a little less contamination, but I guess that wouldn’t matter because you’re blowing the air over the copper, right?

Michael: Well, it is the heat transfer coefficient. You can actually get less surface area because the heat transfer from copper to copper is more efficient than copper to aluminum.

Vincent: Got it. Alright, finally we are going to give away a book. This is an ASM press book, just came out, hardcover, it is a lovely book, you see here, Dickson? It’s cool.

Dickson: Beautifully illustrated.

Vincent: Antisepsis, Disinfection, and Sterilization.

Dickson: Good luck on that.

Vincent: It is by Gerald McDonell and it has wonderful chapters on, wow, there are a lot of chapters here. Let me give you a sense here. Introduction, it has physical disinfection, chemical disinfection, and that goes on for quite a while, metals, antiseptics and antisepsis, physical sterilization, chemical sterilization, mechanisms of action, mechanisms of microbial resistance. 390 pages, and it is not just bacteria, it is viruses, trypanosomes, parasites, fungi, the whole deal. It is a brand new book, never read, never marked up, by ASM press. Send an email to, the subject of the email should be disinfection, and you should write something and tell us about yourself but then we will go through all the emaisl and pick one at random to mail you this book, Antisepsis, Disinfection and Sterilization. You can find TWIM at Apple Podcasts, Please send us your questions and comments And if you like what we do, consider supporting us financially. You can go to to find out how you can do that. Michele Swanson is at the University of Michigan, thank you Michele.

Michele: Thank you and happy new year!

Vincent: Happy new year to you. Michael Schmidt is at the Medical University of South Carolina, thank you Michael.

Michael: Thank you everyone, and happy new year as well!

Vincent: Thanks to the both of you for spending part of your holiday week with TWIM. Dickson Despommier can be found at Thank you, Dickson.

Dickson: Thank you for welcoming me into your fold.

Vincent: You looked lonely out there, so.

Dickson: I was out sensing the quorum.

Vincent: And you said you were gonna be silent, I told you you wouldn’t be silent.

Dickson: You forgot to feed me the siRNA.


Vincent: That’s right. I’m Vincent Racaniello, you can find me at, I would like to thank the American Society for Microbiology for their support of TWIM and Ray Ortega for his technical help. The music you hear on TWIM is by Ronald Jenkees, you can find his work at Thanks for listening everyone, we will see you next time on This Week in Microbiology.


Content on This Week in Microbiology ( is licensed under a Creative Commons Attribution 3.0 License.

Transcribed by Sarah Morgan.