Yeast cells that clump together are better able to grow than lone cells when resources are scarce. The finding suggests a possible stimulus for the evolution of multicellular organisms, say John Koschwanez and his colleagues at Harvard University in Cambridge, Massachusetts.

Some cells of the yeast Saccharomyces cerevisiae do not separate completely after dividing and instead form multicellullar aggregates. The team manipulated this aggregation and the secretion of a yeast enzyme, invertase, that breaks down sucrose, and tracked the cells' growth. Clumps of yeast cells survived when sucrose levels were too low to support individual cells; aggregated cells benefited from sugars that were produced but not consumed by their neighbours.

PLoS Biol. 9, e1001122 (2011)