Chromatium okenii is a Gram-negative bacterium found in water. It belongs to the Purple sulfur bacteria. These bacteria are capable of photosynthesis and use Hydrogen sulfide (HS) as an electron donor for CO reduction and so do not produce oxygen. This type of photosynthesis is called anoxygenic photosynthesis.
Chromatium okenii are just like green plants
They are similar in that they both use photosynthesis, but they do not produce oxygen. The system does not know about photosynthesis of plants.