Specific enrichment culture methods were used to isolate new phototrop
hic heliobacteria (anoxygenic phototrophic bacteria containing bacteri
ochlorophyll g) from various natural samples. A survey of terrestrial
and aquatic habitats yielded heliobacteria only from soils, in particu
lar rice soils, and from certain hot springs. Thirteen nonthermophilic
and 7 thermophilic (capable of growth above 50 degrees C) strains of
heliobacteria were isolated from such habitats and characterized as to
their basic cellular and nutritional properties. Phylogenetic studies
of four strains showed them to be related to known species of helioba
cteria. It is concluded that, unlike phototrophic purple and green bac
teria, heliobacteria are primarily (if not exclusively) terrestrial, e
xcept for hot spring species. This suggests that the ecology of heliob
acteria is fundamentally different from that of other anoxyphototrophs
.