Purple sulfur bacteria Purple sulfur bacteria The purple sulfur bacteria (PSB) are part of a group of Proteobacteria capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in stratified water environments including hot springs, stagnant water bodies, as well as microbial mats in intertidal zones. Unlike plants, algae, and cyanobacteria, purple sulfur bacteria do not use water as their reducing agent, and therefore do not produce oxygen. Instead, they can use sulfur in the form of sulfide, or thiosulfate (as well, some species can use H, Fe, or NO) as the electron donor in
Green algae were acquired from ingested green algae, and in the latter retain a nucleomorph (vestigial nucleus). Green algae are also found symbiotically in the ciliate "Paramecium", and in "Hydra viridissima" and in flatworms. Some species of green algae, particularly of genera "Trebouxia" of the class "Trebouxiophyceae" and "Trentepohlia" (class Ulvophyceae), can be found in symbiotic associations with fungi to form lichens. In general the fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus. "Trentepohlia" is a filamentous green alga that can live independently on humid soil,