Heliobacteria
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. Phototrophy takes place at the cell membrane, which does not form folds or compartments as it does in purple bacteria. Though heliobacteria are phototrophic, they can grow without light by fermentation of pyruvate.
RNA trees place the heliobacteria among the Firmicutes, but they do not stain Gram-positively. They have no outer membrane and like certain other firmicutes, they form heat-resistant endospores, which contain high levels of calcium and dipicolinic acid. Heliobacteria are the only firmicutes known to be phototrophic.
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. Heliobacteria have been found in soils, hot springs, soda lakes and are apparently widespread in the waterlogged soils of paddy fields. They are avid nitrogen fixers, so are probably important in the fertility of paddy fields.Taxonomy
Heliobacteria should not be confused with Helicobacter, which is a genus of bacteria with quite different characteristics.
Family Heliobacteriaceae
- Candidatus Helioclostridium♠ Girija et al. 2006
- *Candidatus Helioclostridium ananthapuram♠ Girija et al. 2006
- Heliorestis Bryantseva et al. 2000
- *H. baculata Bryantseva et al. 2001
- *H. convoluta♠ Asao et al. 2005
- *H. daurensis Bryantseva et al. 2000
- Heliophilum Ormerod et al. 1996
- *Heliophilum fasciatum Ormerod et al. 1996
- Heliobacillus Beer-Romero and Gest 1998
- *Candidatus H. elongatus♠ Girija et al. 2006
- *H. mobilis Beer-Romero and Gest 1998
- Heliobacterium Gest and Favinger 1985
- *H. aridinosum♠ Girija et al. 2006
- *H. chlorum Gest and Favinger 1985
- *H. gestii Ormerod et al. 1996
- *H. modesticaldum Kimble et al. 1996
- *H. sulfidophilum Bryantseva et al. 2001
- *H. undosum Bryantseva et al. 2001
Notes:
♠ Strain found at the National Center for Biotechnology Information but has no standing with the Bacteriological Code as detailed by List of Prokaryotic names with Standing in Nomenclature 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.
