They include plant-associated bacteria such as Bradyrhizobium, a genus of rhizobia associated with some legumes.

It also contains animal-associated bacteria such as Afipia felis, formerly thought to cause cat-scratch disease.

Others are free-living, such as Rhodopseudomonas, a purple bacterium found in marine water and soils.

The strain Rhodopseudomonas palustris DX-1 can generate an electric current with no hydrogen production, a trait being explored in the development of the microbial fuel cell.

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN).