Thiocystis (thigh-owe-cyst-is) is a red sulphur bacterium (or purple sulphur bacterium). It is found in sediments above the reduced zone. It oxidizes hydrogen sulphide producing elemental sulphur which is deposited within the bacterial cell as granules of sulphur. Forms aggregates and individual cells are often hard to distinguish. The cellular nature of these aggregates is hard to determine at first glance. This detail shows that the mass is made of individual cells and the cells have granular inclusions. Phase contrast.