Heliobacteria

Abstract

AbstractHeliobacteria are the most recently discovered of the anoxygenic phototrophic bacteria. Heliobacteria contain bacteriochlorophyllg, a pigment unique to species of this group, and synthesise the simplest photosynthetic complexes of all known phototrophs. Also, unlike all other phototrophs, heliobacteria produce endospores but cannot grow autotrophically. Four genera of heliobacteria are known. Species ofHeliobacterium,HeliobacillusandHeliophilumgrow best at neutral pH, whereas species ofHeliorestisare alkaliphilic.Heliobacterium,HeliobacillusandHeliophilumspecies form one phylogenetic clade whereasHeliorestisspecies form a second within the phylum Firmicutes of the domain Bacteria. Heliobacteria have a unique ecology, being primarily terrestrial rather than aquatic, and some species may have evolved a mutualistic relationship with rice plants. The genome sequence of the thermophileHeliobacterium modesticaldumsupports the hypothesis that heliobacteria are minimalist phototrophs, and because of this, heliobacteria may have played a pivotal role in the evolution of phototrophic bacteria.Key Concepts:Heliobacteria are unlike all known anoxygenic phototrophic bacteria because of their unique bacteriochlorophyll, Gram‐positive phylogeny, and primarily soil habitat.Heliobacteria employ the simplest of all photosynthetic energy‐generating systems and thus their study may yield important clues to when and how photosynthesis evolved.In addition to being phototrophic, heliobacteria are strong nitrogen‐fixing bacteria and possibly associate with plants such as rice in a type of symbiotic association.