Oxalobacter formigenes is a Gram negative oxalate-degrading anaerobic bacterium that was first isolated from the gastrointestinal tract of a sheep in 1985. To date, the bacterium has been found to colonize the large intestines of numerous vertebrates, including humans, and has even been isolated from freshwater sediment. It processes oxalate by decarboxylation into formate, producing energy for itself in the process.