EAST LANSING, Mich. — A team of researchers at Michigan State University has documented the step-by-step process in which organisms evolve new functions.
The results, published in the current issue of Nature, are revealed through an in-depth, genomics-based analysis that decodes how E. coli bacteria figured out how to supplement a traditional diet of glucose with an extra course of citrate. […]
Normal E. coli can’t digest citrate when oxygen is present. In fact, it’s a distinct hallmark of E. coli. They can’t eat citrate because E. coli don’t express the right protein to absorb citrate molecules.
In the Nature paper, Blount and his teammates analyzed 29 genomes from different generations to find the mutational pieces of the puzzle. They uncovered a three-step process in which the bacteria developed this new ability.
The first stage was potentiation, when the E. coli accumulated at least two mutations that set the stage for later events. The second step, actualization, is when the bacteria first began eating citrate, but only just barely nibbling at it. The final stage, refinement, involved mutations that greatly improved the initially weak function. This allowed the citrate eaters to wolf down their new food source and to become dominant in the population. […]
“It wasn’t a typical mutation at all, where just one base-pair, one letter, in the genome is changed,” he said. “Instead, part of the genome was copied so that two chunks of DNA were stitched together in a new way. One chunk encoded a protein to get citrate into the cell, and the other chunk caused that protein to be expressed.”
It’s one thing to witness each the later generations develop the ability to digest a previously inedible food source; it’s another to understand how it happened on a genetic level. It scares me, though, that as this is going on, there are still places in this country in which teaching that this occurs at all is either discouraged or so muddied by religious nonsense that children come out of school with a grasp of science equivalent to someone from rural Pakistan.