This is just amazing: Bacteria evolve a way to share electrons: “

Life is powered by the shuffling of electrons. When organisms break down a food source like a sugar, they’re really extracting high-energy electrons, which they shuffle down through intermediate proteins before they end up in a final electron acceptor. For most of the life we’re familiar with, that acceptor is oxygen. But for various microbes that thrive in the absence of oxygen, a variety of other chemicals are used. 

In the current paper, the authors forced two different species of bacteria to live in an anaerobic environment, and provided them with ethanol as food. Initially, they grew very poorly. After several transfers, however, the rate of growth improved, and small, colored nodules began to appear in the culture, which contained a mix of the two types of bacteria. The authors checked a number of the chemicals that are typically used to transfer electrons in these symbiotic cultures, but saw no evidence of their being used. 

To figure out what was going on, they did whole-genome sequencing, and found only one change: a single base missing in the gene for a protein that regulates RNA production. Making a similar mutation in another strain also allowed those bacteria to form quick-growing nodules. The mutation appears to cause proteins involved in electron transfer to be expressed at increased levels. These proteins end up on pilli, arm-like structures that extend out from the bacteria.