ABSTRACT
Two new taxa of phototrophic heliobacteria are described: Heliobacterium gestii sp. nov. and Heliophilum fasciatum gen. nov. sp. nov. Both organisms were isolated from dry paddy soils. Cells of H. gestii were motile spirilla; cells of H. fasciatum formed cell bundles that were motile as units. Both organisms produced endospores; H. gestii endospores contained dipicolinic acid and elevated levels of calcium. As with other heliobacteria, bacteriochlorophyll g was produced in both organisms and no intracytoplasmic photosynthetic membranes were observed. Growth of H. gestii and H. fasciatum occurred under both photoheterotrophic and chemotrophic conditions; nitrogen fixation also occurred in both organisms. H. gestii and H. fasciatium showed a phylogenetic relationship to the "low GC" line of gram-positive Bacteria, but H. fasciatum was distinct from H. gestii and all other heliobacteria. The ability of H. gestii and H. fasciatum to form endospores might be a significant ecological advantage for survival in their rice soil habitat.
Subject(s)
Bacteria/classification , Bacteria/ultrastructure , Bacterial Physiological Phenomena , Endospore-Forming Bacteria/classification , Endospore-Forming Bacteria/ultrastructure , Bacteria/isolation & purification , Bacteriochlorophylls/chemistry , Bacteriochlorophylls/metabolism , Biological Evolution , Endospore-Forming Bacteria/isolation & purification , Endospore-Forming Bacteria/physiology , Microscopy, Electron , Oryza , Photosynthesis , RNA, Bacterial , RNA, Ribosomal, 16S , Soil Microbiology , Spores, Bacterial/chemistry , Spores, Bacterial/ultrastructureABSTRACT
Conditions are described that support anaerobic dark chemotrophic growth of heliobacteria. Growth was pyruvate-dependent and was best in well-buffered pyruvate media supplemented with yeast extract. Heliobacterial cells grown in darkness synthesized bacteriochlorophyll g and carotenoids and fermented pyruvate to acidic products, CO2, and in some cases, H2. All recognized species of heliobacteria as well as several newly isolated strains were capable of dark anaerobic growth, suggesting that this growth mode may be ecologically important for survival of these organisms in their soil habitat.