Yeast's Secrets

Considering cells must cooperate to multiply, it's a wonder most living things ever progressed beyond the single-cell stage, says Carl Zimmer at The New York Times. But new research from the University of Minnesota's William Ratcliff sheds some light on how multicellular organisms came to be. Using brewer's yeast, Ratcliff and his team raised cell lines, allowing natural selection to favor any new mutation that caused the yeast to settle quickly after being shaken in one flask, and then transferred into a fresh flask. "In a matter of weeks, Dr. Ratcliff noticed, the yeast was sinking fast, forming a cloudy layer at the bottom of the flasks," Zimmer says. "He put the yeast under a microscope and discovered that most of it was no longer growing as single cells. Instead, the broth was dominated by snowflake-shaped clusters of hundreds of cells stuck together." When the researchers isolated cells from these clusters and allowed them to grow anew, they found that these cells immediately formed new groupings. "Dr. Ratcliff suspects that the transformation of the yeast in his lab may offer hints about how animals and other lineages became multicellular hundreds of millions of years ago," Zimmer adds.