This episode of evolution is entirely of our own doing. In 1936, a chemical called pentachlorophenol went on the market. It was hugely popular as a way to preserve telephone poles and lumber against fungi and termites. Unfortunately, it also turned out to be toxic to humans, and once it got into the soil it could contaminate the ground for years. That’s because the molecule–five chlorine atoms decorating a ring of carbon atoms–had not previously existed in nature. Microbes had not evolved to feed on it before. It was as toxic to them as it was to us.
Starting in the 1970s, however, scientists discovered some microbes that had begun to feed on pentachlorophenol. Pollution-eating bugs are popular in microbiology circles, because they can sometimes be deployed to clean up our messes. So a number of scientists have spent recent years dissecting the pentachlorophenol-eaters. Last year, for example, researchers published the genome of one such species, Sphingobium chlorophenolicum, which had been discovered in pentachlorophenol-laced soil in Minnesota in 1985.
When you first learn how Sphingobium eats pentachlorophenol, it inspires that same awe that eyes and oaks do. It uses a series of enzymes to pick off the chlorine atoms one at a time, like a gorilla removing spines from nettles. And yet, for all the complexity of Sphingobium‘s biochemistry, it does a pretty lousy job of feeding on pentachlorophenol.