Heliobacteria

Heliobacteria are a unique subset of prokaryotic bacteria that process light for energy. Distinguishable from other phototrophic bacteria, they utilize a unique photosynthetic pigment, bacteriochlorophyll g and are the only known Gram-positive phototroph.<ref>Template:Cite journal</ref> They are a key player in symbiotic nitrogen fixation alongside plants, and use a type I reaction center like green-sulfur bacteria.<ref>Template:Cite book</ref><ref>Template:Cite book</ref>

RNA trees place the heliobacteria among the Bacillota.<ref name=":0" /> They have no outer membrane and like certain other Bacillota (Clostridia), they form heat-resistant endospores, which contain high levels of calcium and dipicolinic acid. Heliobacteria are the only Bacillota known to be phototrophic.

Metabolism

The heliobacteria are phototrophic: they convert light energy into chemical energy using a type I reaction center.<ref>Heinickel and Golbeck 2007</ref><ref>Template:Cite journal</ref> The primary pigment involved is bacteriochlorophyll g, which is unique to the group and has a unique absorption spectrum; this gives the heliobacteria their own environmental niche.<ref name=":0">Template:Cite book</ref> Phototrophic processes take place at the cell membrane, which does not form folds or compartments as it does in purple bacteria. Though heliobacteria are phototrophic, they can create energy without light using pyruvate fermentation, which generates significantly less energy than it could with light.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Heliobacteria are photoheterotrophic, requiring organic carbon sources, and they are exclusively anaerobic.<ref name=":0" /> Bacteriochlorophyll g is inactivated by the presence of oxygen, making them obligate anaerobes (they cannot survive in aerobic conditions). Heliobacteria have been found in soils,<ref name=":1">Template:Citation</ref> hot springs,<ref>Template:Cite journal</ref> soda lakes<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> and are common in the waterlogged soils of paddy fields.<ref name=":1" /> They are avid nitrogen fixers, so are probably important in the fertility of paddy fields.<ref name=":1" /> Heliobacteria are mainly terrestrial phototrophs, contrary to the multitudes of others that are aquatic, and often form mutualistic relationships with the plants near them.<ref>Template:Cite journal</ref>

Taxonomy

Heliobacteria should not be confused with Helicobacter, which is a genus of bacteria with quite different characteristics.

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)<ref name=LPSN>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and National Center for Biotechnology Information (NCBI).<ref name=NCBI>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

16S rRNA based LTP_10_2024<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>	120 marker proteins based GTDB 09-RS220<ref name="about">{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref name="tree">{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref name="taxon_history">{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>

See also

• List of bacterial orders
• List of bacteria genera

Further reading

• Gest H & Favinger J L (1983) Arch Microbiol 136:11-16.
• Madigan M T (1992) In Balows et al. (eds) The Prokaryotes pp. 1981–1992 Springer New York.
• Madigan M T & Ormerod J G (1995) In Blankenship et al. (eds) Anoxygenic Photosynthetic Bacteria pp 17–30. Kluwer Academic Publishers New York.
• Ormerod J G et al. (1996) Arch Microbiol 165:226-234.
• Madigan M T, Martinko J M, Dunlap P V, Clark D P. (2009). Brock Biology of Microorganisms 12th edition, p. 453-454
• Heinnickel M & Golbeck J H (2007) Photosynthesis Research 92:35-53