Thiothrix annulata is a filamentous sulfur-oxidizing gammaproteobacterium in the family Thiotrichaceae, forming sheathed trichomes that attach to substrates in sulfide-rich aquatic environments. It oxidizes reduced sulfur compounds as an energy source and stores elemental sulfur granules within its cells, giving colonies a whitish appearance. It inhabits sulfur springs, sewage systems, and freshwater streams with elevated sulfide levels.