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. They are a key player in symbiotic nitrogen fixation alongside plants, and share a reaction center with green-sulfur bacteria.
RNA trees place the heliobacteria among the Firmicutes. They have no outer membrane and like certain other firmicutes (Clostridia), they form heat-resistant endospores, which contain high levels of calcium and dipicolinic acid. Heliobacteria are the only firmicutes known to be phototrophic.
Metabolism.
The heliobacteria are phototrophic: they convert light energy into chemical energy using a type I reaction center. 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. 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.
Heliobacteria are photoheterotrophic, requiring organic carbon sources, and they are exclusively anaerobic. 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, hot springs, soda lakes and are common in the waterlogged soils of paddy fields. They are avid nitrogen fixers, so are probably important in the fertility of paddy fields. Heliobacteria are mainly terrestrial phototrophs, contrary to the multitudes of others that are aquatic, and often form mutualistic relationships with the plants near them.
Taxonomy.
Heliobacteria should not be confused with "Helicobacter", which is a genus of bacteria with quite different characteristics.
Family Heliobacteriaceae
Notes:
♠ Strain found at the National Center for Biotechnology Information (NCBI) but has no standing with the Bacteriological Code (1990 and subsequent Revision) as detailed by List of Prokaryotic names with Standing in Nomenclature (LPSN) as a result of the following reasons:
• No pure culture isolated or available for prokaryotes.
• Not validly published because the effective publication only documents deposit of the type strain in a single recognized culture collection.
• Not approved and published by the International Journal of Systematic Bacteriology or the International Journal of Systematic and Evolutionary Microbiology (IJSB/IJSEM).