Purple Sulfur Bacteria
The PSB is an interesting phototrophic organism that uses sunlight to power the conversion of sulfides (including hydrogen sulfide) into sulfur. The carbon source for their growth is usually carbon dioxide, but they can also assimilate carbon from organic acids or alcohols. They are obligate phototrophs, so they tend to be more common in summer months. As they remove H2S and some volatile organic acids, the PSB can be useful in lowering odor problems with lagoons.
Purple Non-Sulfur Bacteria
These are found in lagoons with lower sulfide (H2S) levels and can use organic compounds as an electron donor. They are still found in anoxic environments and use photosynthetic reactions to obtain energy.