Fig. 1.

Microbes and cells from multicellular organisms have similar metabolic phenotypes under similar environmental conditions. Unicellular organisms undergoing exponential growth often grow by fermentation of glucose into a small organic molecule such as ethanol. These organisms, and proliferating cells in a multicellular organism, both metabolize glucose primarily through glycolysis, excreting large amounts of carbon in the form of ethanol, lactate, or another organic acid such as acetate or butyrate. Unicellular organisms starved of nutrients rely primarily on oxidative metabolism, as do cells in a multicellular organism that are not stimulated to proliferate. This evolutionary conservation suggests that there is an advantage to oxidative metabolism during nutrient limitation and nonoxidative metabolism during cell proliferation.