Carl Zimmer in his blog, The Loom:
Usually when you hear about the rapid evolution of bacteria, the story is typically some grim tale of antibiotic resistance or the emergence of some pathogen once restricted to animals. Here’s a nicer narrative, but no less instructive. In tomorrow’s New York Times I have an article about yogurt, and how the bacteria in its culture have been undergoing drastic genomic change since the stuff was invented some 5000 years ago.
I report on a new study on Lactobacillus bulgaricus, found in many yogurt cultures. (The paper comes out some time this week in PNAS.) The analysis, based on the microbe’s newly sequenced genome, suggests that the bacteria descend from microbes that originally fed on plants. Some of them fell accidentally into some herder’s milk, it seems, and happened to clot it and kept it from spoiling. Since then, people have been transferring yogurt to fresh milk time and again, and the effect has been like running a long-term experiment on the evolution of bacteria.
More here.