Nietzsche Undone: An Infection that Doesn’t Kill You Can Make You Weaker

The German philosopher, Friedrich Nietzsche, is known for a number of ideas among which a particularly oft-quoted one is, “That which does not kill us makes us stronger” (https://www.goodreads.com/quotes/30-that-which-does-not-kill-us-makes-us-stronger). A recent report in Cell (Fonseca et al., 2015) offers evidence that in the context of infection and immunity, the above aphorism may not be a reliable guide to reality. (more…)

Phenotypic and Genotypic Variation of a Fungal Pathogen Powered by Codon Ambiguity and Degenerate Translation

The term “genetic code” is associated with a measure of ambiguity.  For molecular biologists, “genetic code” has historically referred to a table that provides for each messenger RNA ribonucleotide triplet the corresponding amino acid that is incorporated into the growing end of a nascent polypeptide chain, i.e. the translation from RNA sequence to protein sequence.  In colloquial parlance, “genetic code” is frequently used to refer to all or part of the deoxribonucleotide sequence of a genome.  A recent paper, published online ahead of print in Proceedings of the National Academy of Sciences (Bezerra et al., PNAS, 2013) demonstrates that this semantic ambiguity can have a counterpart in the ribosomal interpretation of the genetic code, using the technical molecular biological meaning of the latter term. (more…)

Environmental factors driving susceptibility to depression; psychosocial or microbiological?

By Graham Rook

Chronic inflammatory disorders (allergies, autoimmunity, IBD) have increased dramatically in developed countries. But depression is strongly associated with these disorders and should therefore be increasing in parallel. While there is no universal agreement, there is evidence that rates of depression are indeed increasing (discussed and referenced in Raison et al., 2010). Moreover, moving from the developing world to the U.S. increases the risk. For example, Mexican immigrants to the U.S. have rates of depression similar to those seen in Mexico. However, individuals of Mexican descent born in the U.S. have higher rates that are equivalent to those of the U.S. population at large, suggesting that it is the American lifestyle rather than acculturation shock that accounts for the increase (Vega et al., 2004). Interestingly there is also a significantly higher risk of mood and anxiety disorders in urban populations, compared to rural ones (Peen et al., 2010).

These findings all imply an environmental trigger that is more prevalent in developed and urban situations than in undeveloped and rural ones. But what is this environmental trigger? (more…)

Phenotypic noise and the evolution of virulence

Commentary on: M. Ackermann, B. Stecher, N. E. Freed, P. Songhet, W.-D. Hardt, and M. Doebeli (2008) Self-destructive cooperation mediated by phenotype noise. Nature 454:987-9

One of the most exciting developments in microbial population biology over the past few years is the recognition that high levels of phenotypic noise – in which genetically identical microbes express different genes and manifest different phenotypes despite a common environment – is widespread in bacterial populations and that this noise plays an important role in bacterial evolutionary ecology (e.g. Elowitz et al. 2002, Balaban et al. 2004, Rosenfeld et al. 2005, Acar et al. 2008, Veening et al. 2008). I have always thought that the best explanations for this phenomenon involve bet hedging in uncertain environments (Seger and Brockmann 1987), and indeed this bet-hedging perspective has been well supported by mathematical modeling (e.g. Thattai and van Oudenaarden 2004, Kussell et al. 2005).

But in this week’s issue of Nature, Martin Ackermann and colleagues propose an alternative explanation (more…)