Hey Mom, Don't You Recognize Me? (or, They Must Have Had a Really Big Autoclave)

In this week's Science, Gibbs et al. report their findings of well, I don't know how else to say this, but a shit-ton of genetic screening that they did to identify the genetic basis of self-identity in a swarming bacterium (See this page for more info and photos of the bacteria in attack mode.) The bug of focus was Proteus mirabilis, a bacterium that is responsible for urinary tract infection, kidney stones and other types of infection in humans. What's cool is that if different strains of these motile bacteria come into contact on an agar plate, one can observe a visible boundary between them. Sometimes, there is even microbial warfare, with one strain secreting proteins capable of killing the other. Up until now, though, no one knew how one strain recognized another as either a "chip off the old block" or a potential enemy (they're too small to wear blue and red bandanas). Gibbs and company screened 3600 (!) mutants of a strain of P. mirabilis, each generated with transposons randomly integrated into the bacterial genome. They identified one region that was particularly war-mongering and christened it "ids" - identification of self. They mapped the mutation to a cluster of six genes and then set about doing even more screening to knock out the various individual genes and then replace them systematically on plasmids. They then go on to do even more experiments (read the article if you're having trouble falling asleep tonight) to tease apart the exact mechanism by which these genes allow the bacteria to tell what strain they are and then sequence this region in completely different isolates of P. mirabilis. In the end, though, they are unable to identify any specific products from these genes, so the mechanism is still a mystery. Nonetheless, it is an important step in understanding cell-cell signaling in microbes and a very basic process of producing and maintaining variation and no doubt will soon find its way into new genetics textbooks as a nifty example.