Хлоробиум бактериясы: сипаттамасы мен маңызы

Genus of bacteria

Chlorobium is a genus of green sulfur bacteria. They are photolithotrophic oxidizers of sulfur and most notably utilise a noncyclic electron transport chain to reduce NAD+. Photosynthesis is achieved using a Type 1 Reaction Centre using bacteriochlorophyll (BChl) a. Two photosynthetic antenna complexes aid in light absorption: the Fenna Matthews Olson complex ("FMO", also containing BChl a), and the chlorosomes which employ mostly BChl c, d, or e. Hydrogen sulfide is used as an electron source and carbon dioxide its carbon source. Chlorobium species exhibit a dark green color; in a Winogradsky column, the green layer often observed is composed of Chlorobium. This genus lives in strictly anaerobic conditions below the surface of a body of water, commonly the anaerobic zone of a eutrophic lake. Chlorobium species are thought to have played an important part in mass extinction events on Earth. If the oceans turn anoxic (due to the shutdown of ocean circulation) then Chlorobium would be able to out compete other photosynthetic life. They would produce huge quantities of methane and hydrogen sulfide which would cause global warming and acid rain. This would have huge consequences for other oceanic organisms and also for terrestrial organisms. Evidence for abundant Chlorobium populations is provided by chemical fossils found in sediments deposited at the Cretaceous mass extinction.

Comparative genomic analysis has led to the identification of 2 conserved signature indels which are uniquely found in members of the phylum Chlorobiota (formerly Chlorobi) and are thus characteristic of the phylum. The first indel is a 28 amino acid insertion in DNA polymerase III and the second is a 12 to 14 amino acid insertion in alanyl tRNA synthetase. These indels are not found in any other bacteria and thus serve as molecular markers for the phylum. In addition to the conserved signature indels, 51 proteins which are uniquely found in members of the phylum Chlorobiota. 65 other proteins have been identified which are unique to the Chlorobiota phylum, however these proteins are missing in several Chlorobiota species and are not distributed throughout the phylum with any clear pattern. This means that significant gene loss may have occurred, or the presence of these proteins may be a result of horizontal gene transfer. Of these 65 proteins, 8 are found only in Chlorobium luteolum and Chlorobium phaeovibrioides. These two species form a strongly supported clade in phylogenetic trees and a close relationship between these species is further supported by the unique sharing of these 8 proteins.