The order halanaerobiales, and the families halanaerobiaceae and halobacteroidaceae

The order Halanaerobiales, families Halanaerobiaceae and Halobacteroidaceae, consists of obligatory anaerobic, moderately halophilic bacteria that require NaCl concentrations between 0.5 and 3.4 M for optimal growth. Representatives have been isolated from anaerobic sediments of salt lakes worldwide, from brines associated with oil reservoirs, and also from fermented salted foods. Some species are thermophilic or alkaliphilic. Although phylogenetically affiliated with the low G+C branch of the Firmicutes, the cells show a Gram-negative wall structure, and most species stain Gram-negative. Some representatives of the Halobacteroidaceae produce endospores. Most species ferment carbohydrates to acetate, ethanol, H₂, CO₂, and other fermentation products. Within the Halobacteroidaceae, a greater metabolic diversity is found, with some species displaying a homoacetogenic metabolism; growth by anaerobic respiration using different electron acceptors including nitrate, trimethylamine.-oxide, selenate, arsenate, or Fe(III); or chemolithoautotrophic growth on hydrogen and elemental sulfur.