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 (H₂S) as an electron donor for CO₂ 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.

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