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Purple sulfur bacteria
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<p>The purple sulfur bacteria (PSB) are part of a group of <a href="/facts/Pseudomonadota/ggjeK6II">Pseudomonadota</a> capable of <a href="/facts/Photosynthesis/TMV7w693">photosynthesis</a>, collectively referred to as <a href="/facts/Purple_bacteria/CTWwb0PU">purple bacteria</a>. They are <a href="/facts/Anaerobic_organism/bhQnlqCq">anaerobic</a> or <a href="/facts/Microaerophilic/J4dHmegH">microaerophilic</a>, and are often found in stratified water environments including <a href="/facts/Hot_spring/YrzFykH1">hot springs</a>, <a href="/facts/Stagnant_water/1cbBED8V">stagnant water</a> bodies, as well as microbial mats in intertidal zones. Unlike <a href="/facts/Plantae/X5BMDMvS">plants</a>, <a href="/facts/Algae/U1ftVKU3">algae</a>, and <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a>, purple sulfur bacteria do not use <a href="/facts/Water/0lkXnJPK">water</a> as their <a href="/facts/Reducing_agent/CtfSGVXC">reducing agent</a>, and therefore do not produce <a href="/facts/Oxygen/acyn6o8r">oxygen</a>. Instead, they can use sulfur in the form of sulfide, or <a href="/facts/Thiosulfate/LYu0KhDu">thiosulfate</a> (as well, some species can use H2, Fe2+, or NO2−) as the electron donor in their <a href="/facts/Photosynthetic/TMV7w693">photosynthetic</a> pathways. The sulfur is <a href="/facts/Redox/Pyd5RVcj">oxidized</a> to produce granules of elemental <a href="/facts/Sulfur/IK0amTfM">sulfur</a>. This, in turn, may be oxidized to form <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a>. </p><p>The purple sulfur bacteria are largely divided into two families, the <a href="/facts/Chromatiaceae/cJoJjN8N">Chromatiaceae</a> and the <a href="/facts/Ectothiorhodospiraceae/eJTTAvvY">Ectothiorhodospiraceae</a>, which produce internal and external sulfur granules respectively, and show differences in the structure of their internal membranes. They make up part of the order Chromatiales, included in the <a href="/facts/Gammaproteobacteria/2ISNVT8r">Gammaproteobacteria</a>. The genus <i><a href="/facts/Halothiobacillus/05QDrphE">Halothiobacillus</a></i> is also included in the Chromatiales, in its own family, but it is not photosynthetic. </p>