Any of a diverse group of bacteria that are capable of metabolizing sulfur and its compounds and are important in the sulfur cycle. Members of the genus Thiobacillus, widespread in marine and terrestrial habitats, react with sulfur to produce sulfates useful to plants; in deep ground deposits they generate sulfuric acid, which dissolves metals in mines and corrodes concrete and steel. Desulfovibrio desulficans reduces sulfates in waterlogged soils and sewage to hydrogen sulfide, a gas with the common rotten-egg odour.
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Green sulfur bacteria are non-motile (except Chloroherpeton thalassium, which may glide) and come in spheres, rods, and spirals. Photosynthesis is achieved using bacteriochlorophyll (BChl) c, d, or e, in addition to BChl a and chlorophyll a, in chlorosomes attached to the membrane. They use sulfide ions, hydrogen or ferrous iron as an electron donor and the process is mediated by the type I reaction centre and Fenna-Matthews-Olson complex. Elemental sulfur deposited outside the cell may be further oxidized. By contrast, the photosynthesis in plants uses water as electron donor and produces oxygen.
Chlorobium tepidum has emerged as a model organism for the group, and although only ten genomes have been sequenced, these are quite comprehensive of the family's biodiversity. Their 2-3 Mb genomes encode 1750-2800 genes, 1400-1500 of which are common to all strains. The apparent absence of two-component histidine-kinases and response regulators suggest limited phenotypic plasticity. Their small dependence on organic molecule transporters and transcription factors also indicate that these organisms are adapted to a narrow range of energy-limited conditions, an ecology shared with the simpler cyanobacteria, Prochlorococcus and Synechococcus
A species of green sulfur bacteria has been found living near a black smoker off the coast of Mexico at a depth of 2,500 meters beneath the surface of the Pacific Ocean. At this depth, the bacterium, designated GSB1, lives off the dim glow of the thermal vent since no sunlight can penetrate to that depth.