Need to feed could have driven single cells to evolve into colonies

By ED YONG - NOT EXACTLY ROCKET SCIENCE
Added: Wed, 10 Aug 2011 00:25:43 UTC

Most life on this planet goes about their business as single cells. Only rarely do these singletons unite in cooperative societies, creating bigger and more complex living things, from trees to humans. This transition from single-celled to ‘multicellular’ life is one of the most important transitions in the evolution of life on Earth and it has happened many times over.

There are two main routes to a multicellular life. Single cells can merge together, and some modern species recap how this might have happened. Individual slime moulds join to form mobile slugs, while myxobacteria can merge into predatory swarms. Alternatively, cells can multiply but remain attached, staying united in their division. The choanoflagellates, possibly the closest living relatives of animals, can do this, creating simple colonies from single cells.

So we have a reasonable, if basic, understanding of how multicellular creatures first evolved. But we’re still largely in the dark about why. What benefit did cells gain from sticking together, rather than swimming solo? John Koschwanez from Harvard University thinks he has one answer: by sticking together, clumps of cells became better at foraging for nutrients. The multicellular life was a well-fed one.

Koschwanez worked with the yeast, Saccharomyces cerevisiase, a darling of bakers, brewers and geneticists alike. S.cerevisiae usually lives as a single cell. It feeds by slobbering digestive enzymes into its environment and absorbing the liberated nutrients. For example, it secretes an enzyme called invertase that breaks the sugar sucrose in half, forming glucose and fructose. It then absorbs these smaller sugars.