What type of photosynthesis does not produce oxygen?

What type of photosynthesis does not produce oxygen? Anoxygenic photosynthesis is the form of photosynthesis that does not produce molecular oxygen. It is carried out by certain bacteria that use electron donors other than water, such as hydrogen sulfide, hydrogen, or ferrous iron.

In oxygenic photosynthesis, plants, algae, and cyanobacteria split water and release oxygen as a by-product. Anoxygenic phototrophs avoid that water-splitting step. Depending on the organism and electron donor, their by-products can include elemental sulfur, sulfate, or other oxidized compounds instead of oxygen.

These bacteria use light energy to generate an electrochemical gradient and make ATP. Many use bacteriochlorophyll rather than the chlorophyll found in plants and cyanobacteria. Their reaction centers generally represent either type I or type II systems, rather than the paired arrangement used by oxygenic phototrophs.

Anoxygenic photosynthesis is especially important in anaerobic environments such as illuminated sediments, sulfur-rich waters, and some microbial mats. CAM and C4 photosynthesis are not oxygen-free alternatives: they are carbon-fixation strategies used by plants that still perform oxygenic photosynthesis.