Chromatium okenii is a Gram-negative bacterium found in water. It is a purple sulfur bacterium. These bacteria are capable of photosynthesis and use Hydrogen sulfide (H<sub>2</sub>S) as an electron donor for CO<sub>2</sub> reduction and so do not produce oxygen. This type of photosynthesis is called anoxygenic photosynthesis. Chromatium okenii is anaerobic and the cells are slightly curved or straight rods.