Sulfate reducing bacteria that create waste usable by other organisms in a deep subsurface, radioactive environment. This is way cool.

"In a way, Firmicutes serve the same function as photosynthetic organisms, such as plankton and trees at Earth's surface, that capture sunlight energy ultimately to the benefit of everything and everyone else. In the deep subsurface case, Firmicutes species are the producers, capturing the energy of radiation-borne hydrogen gas to support microbial communities."