Heliobacteria

The heliobacteria are phototrophic, that is to say, they convert light energy into chemical energy by photosynthesis; they use a PSI type 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. Photosynthesis takes place at the cell membrane, which does not form folds or compartments as it does in purple phototrophic bacteria.

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 (clostridia) they form heat resistant endospores. They are the only firmicutes known to conduct photosynthesis.

Heliobacteria are photoheterotrophic, requiring organic carbon sources, and they are exclusively anaerobic. So far heliobacteria have only been found in soils, and are apparently widespread in the waterlogged soils of paddy fields. They are avid nitrogen fixers and are therefore probably important in the fertility of paddy fields.