All moral rights asserted. Recolouring or alteration of the image is prohibited without permission. Heliobacteria, coloured scanning electron micrograph (SEM) .The heliobacteria are phototrophic, that is they convert light energy into chemical energy. They use a type I reaction centre and the primary pigment involved is bacteriochlorophyll g, which is unique to the group and has a unique absorption spectrum. 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. Heliobacteria are photoheterotrophic, requiring organic carbon sources, and they are exclusively anaerobic. Heliobacteria have been found in soils, hot springs, soda lakes and are apparently widespread in the waterlogged soils of paddy fields. They are nitrogen fixers, so are probably important in the fertility of paddy fields. : x3300 when printed at 15 centimetres wide.