Those of you with a biological education know well the λ phage and its host E. coli and the various life-history pathways that characterize interaction between the two.1 So, I was surprised to see this article in PLOS today, Population Fitness and the Regulation of Escherichia coli Genes by Bacterial Viruses (those of you more in the know are surely not surprised). One of my favorite sayings is J.B.S. Haldane’s “fitness is a bugger,” as it expresses to me the difficulties of the concept, and the issues with talking about it without being swamped by a swarm of qualifications, caveats and provisional conjectures. The authors in the paper above suggest that during the lysogenic phase the λ repressor factor, cI, might actually bind to regions of the E. coli genome and so downregulate transcription of products which have metabolic implications. In short, in some environments infection might increase the “fitness” of a bacterial lineage (measured in doubling time). The authors point to a clustering of homologous regions to the λ operator sites as evidence for positive selection (one is a coincidence, but seven?).
Obviously stuff like this is relevant in the abstract as understanding a “simple” organism like E. coli and its relationship to its pathogens can flesh out broader principles that are important in understanding “higher” organisms. Additionally, it seems that humans have an an order of magnitude more bacteria within their bodies (mostly the gut) than they have somatic cells!2 Some of the parasites infecting us are most peculiar, for instance, the bizarre cat parasites which seem to alter individual behavior….
1 – For those of you who don’t want to google, λ infects E. coli and either goes “lytic,” where the infection is virulent and the bacteria dies to release the next generation of phage, or “lysogenic,” where the λ inserts itself into the bacterial genome and hangs around until an opportune time to make a break. It is a canonical biological system that elucidates the complexities involved even in the genetic and physiological interaction between virus and its host bacteria.
2 – Bacteria are important in digestion too, there are certain vitamins, like B12 and K, that don’t seem to get produced in “sterile” organisms, so they need nutritional supplements.
Posted by razib at 06:02 PM