Howard Berg is a physicist turned systems biologist, and he's been a systems biologist long before it was trendy to be one. He's one of the smartest systems biologists around, and a nice guy too (one who was nice enough to sit down for lunch next to an alone, confused, awkward grad student who I'm sure came off as a tremendously boring person...) Berg has devoted his career to understanding information processing in E. coli, and this week in PNAS he describes a physical model of how E. coli senses food in its environment. E. coli's major challenge is living life at low Reynolds Number (PDF):

If you are at very low Reynolds number, what you are doing at the moment is entirely determined by the forces that are exerted on you at that moment, and by nothing in the past.

E. coli swims, but it can't coast - it's like a human swimming in a pool of molasses. In that environment, E. coli has to somehow chase down food. Berg's team has built a physical model of how the protein machinery of E. coli's food-sensing signal processing pathway works to process a variety of environmental signals. This should be the subject of a much more involved post, but in the meantime, check out Berg's paper.