Excerpt from Yeast Experiment Hints at a Faster Evolution From Single Cells
By Carl Zimmer
“The transition to multicellular life has long intrigued evolutionary biologists. The cells in our bodies have evolved to cooperate with exquisite precision. The human body has more than 200 types of cells, each dedicated to a different job. And a vast majority of the 100 trillion cells in our bodies sacrifice their own long-term legacy: Only eggs and sperm have a chance to survive our own death.
These demands for cooperation and sacrifice ought to make it hard for single-celled life to become multicellular. Yet animals, plants and other life forms have evolved bodies. “We know that multicellularity has evolved in different lineages at least 25 times in the history of life,” said William Ratcliff, a postdoctoral researcher at the University of Minnesota.
Dr. Ratcliff and his adviser, Michael Travisano, are experts in experimental evolution. They design experiments in which microbes can evolve interesting new traits within weeks.
“We were sitting in his office drinking coffee, talking about what would be the coolest thing you could do in the lab,” Dr. Ratcliff said. “O.K., the origin of life would be too hard. But other than the origin of life, what would be the coolest thing?” They decided it would be observing single-celled microbes evolving a primitive form of multicellularity.
The scientists designed an experiment with brewer’s yeast, which normally lives as single cells, feeding on sugar and budding off daughter cells to reproduce.”
Here is a link, to actual the PNAS Paper: Experimental evolution of multicellularity
Also another link on yeast multicellularity: Sucrose Utilization in Budding Yeast as a Model for the
Origin of Undifferentiated Multicellularity
Moderators Note: The type of selection they are doing is s simple test that enriches for large clumps of cells that fall out of solution easily, called flocculation. This quality is especially important to brewers and wine makers and can be especially important for the big commercial producers. As a yeast researcher, my personal bias is that this type of selection is due to prion forms of particular proteins involved in mediating flocculation ( [MOT3+]. In Prions are a common mechanism for phenotypic inheritance in wild yeasts the authors propose that induced meta-stable prions are helping to drive evolution as precursors to eventual genetic alterations if specific conditions persist. These types of multicellular clumps will arise spontaneously under nutrient limiting conditions, most likely as a bet-hedging strategy to diversify and adapt dynamically to stressful environmental conditions.
Prion Positive Wine Yeast Aggregates, 40X Celestron - Gordon Walker, Bisson Lab