Reed writes:

Dear Vincent, Elio, Michael, and Michelle,

I’ve just recently finished TWiM number 133 and wanted to comment about the use of the term “secondary metabolite” throughout the episode and often in the primary literature. Michael pointed out that a secondary metabolite is a molecule that is produced by an organism as it reaches stationary phase.

This is actually one of several characteristics that are used to define what a secondary metabolite is. Other common features are that secondary metabolites are “small” molecular weight compounds, they are not involved in the normal growth of an organism, and that they are dispensable for growth and fitness of the producing organism.

However, while many of these molecules are non-essential under laboratory conditions, they may be critical for survival under natural conditions. For example, siderophores are critical for scavenging iron under iron-replete conditions. Pyocyanins produced by Pseudomonas aeruginosa are involved in redox homeostasis. Bacillaene produced by Bacillus subtilis is essential for defense against lysis caused by Streptomyces sp. Mg1 and predation by Myxococcus xanthus. Lugdunin highlighted in the episode is another such case.

Additionally, many of these molecules are produced during multiple growth phases and are not exclusively limited to stationary phase. Taken together, these few examples illustrate that secondary metabolites may be far from “secondary” in their physiological importance. It is for these reasons and more that many have taken to calling these wonderful molecules “specialized metabolites”!

Thank you for the podcast!

Anthony writes:

He withered away for 7 years. Doctors didn’t realize his passion was killing him.


According to the paper, when doctors initially tried diagnosing the man’s illness, they overlooked his daily hobby: playing the bagpipes.

Tests conducted on the man’s bagpipes found a slew of fungi and yeast living inside the musical instrument.

Inside the air bag was a mixture of Paecilomyces variotti, Fusarium oxysporum, Rhodotorula mucilaginosa,and Penicillium species. In a petri dish, they formed a psychedelic swirl of green, orange and red mold.

Henrik writes:


thanks for providing so much information!

I have a mast cell activation syndrome and recently was by Prof. Dr De Meirleir in Brussel to look for chronic infections as a possible cause for mast cell dysfunction. He found that I have positive serology for Tularemia, so it seems that I was in contact with the any of the F. organisms.

He did some follow up tests I will only get to know next month.

My question is: Can the organism F.T. establish chronic infections or will the host either always die or kill the pathogen completely?

Thank you very much,


Katy Bosio’s reply:

There have been a few reports of chronic infections with Tularemia, but I think those were largely restricted to the early days of antibiotic therapy (see Public Health Reports, 1926, 41:1341) and were symptomatic.  They also started with a known exposure to F. tularensis.

It sounds as though the listener may be asking if F. tularensis can cause sub-clinical disease, i.e. infection without detected signs of illness.  There is not much data on this either, but there have been some reports suggesting that it is possible (Emerging Infectious Diseases, 2010, 16(2); Emerging Infectious Diseases, 2015, 21(12)).  



Catharine (Katy) M. Bosio, PhD

Senior Investigator

Immunity to Pulmonary Pathogens Section

Laboratory of Bacteriology

Rocky Mountain Laboratories


Hamilton, MT

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