Green sulfur bacteria

The green sulfur bacteria are a family of obligately anaerobic photoautotrophic bacteria. Most closely related to the nonetheless distant Bacteroidetes, they are accordingly assigned their own phylum.

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 bacteria, designated GSB1, lives off the dim glow of the thermal vent since no sunlight can penetrate to that depth.