The family Chlorobiaceae

Since the discovery of the green sulfur bacteria and the first description by Larsen (1952), this group of bacteria has gained much interest because of a number of highly interesting features. These include the unique structures of the photosynthetic apparatus and the presence of small organelles, the chlorosomes, which act as light-harvesting antenna. Chlorosomes are very powerful light receptors that can capture minute amounts of light and enable the green sulfur bacteria to perform photosynthesis and to grow at very low-light intensities. This has important ecological consequences, because the efficient light harvesting determines the ecological niche of these bacteria at the lowermost part of stratified environments, where the least of light is available. Furthermore, the strict dependency on photosynthesis to provide energy for growth and the obligate phototrophy of the green sulfur bacteria together with their characteristic sulfur metabolism has provoked much interest in their physiology, ecology, and genomics. The oxidation of sulfide as the outmost important photosynthetic electron donor of the green sulfur bacteria involves the deposition of elemental sulfur globules outside the cells and separates the process of sulfide oxidation to sulfate clearly into two steps. In the phylogenetic-based taxonomy, the green sulfur bacteria are treated as family Chlorobiaceae with the genera Chlorobium, Chlorobaculum, Prosthecochloris, and Chloroherpeton