ANAEROBIC-BACTERIA FROM HYPERSALINE ENVIRONMENTS

Strictly anaerobic halophiles, namely fermentative, sulfate-reducing, homoacetogenic, phototrophic, and methanogenic bacteria are involved i n the oxidation of organic carbon in hypersaline environments. To date , six anaerobic fermentative genera, containing nine species, have bee n described. Two of them are homoacetogens. Six species belong to the family Haloanaerobiaceae, as indicated by their unique 16S rRNA oligon ucleotide sequences. Desulfohalobium retbaense and Desulfovibrio halop hilus represent the only two moderately halophilic sulfate reducers so far reported. Among anoxygenic phototrophic anaerobes, a few purple b acteria with optimal growth at salinities between 6 and 11% NaCl have been isolated from hypersaline habitats. They belong to the genera Rho dospirillum, Chromatium, Thiocapsa, and Ectothiorhodospira. The common est organisms isolated so far ape Chromatium salexigens, Thiocapsa hal ophila, and Rhodospirillum salinarum. Extremely halophilic purple bact eria have most commonly been isolated from alkaline brines and require about 20 to 25% NaCl for optimal growth. They belong to the family Ec tothiorodhospiraceae. Their osmoregulation involves synthesis or uptak e of compatible solutes such as glycine-betaine that accumulate in the ir cytoplasm. The existence of methanogens in hypersaline environments is related to the presence of noncompetitive substrates arch as methy lamines, which originate mainly from the breakdown of osmoregulatory a mines. Methanogenesis probably does nor contribute to the mineralizati on of carbohydrates at NaCl concentrations higher than 15%. Above this concentration, sulfate reduction is probably the main way to oxidize H-2 (although at rates too low to use rip all the H-2 formed) and occu pies a terminal function in the degradation of carbohydrates. Three ge nera and five species of halophilic methylotrophic methanogens have be en reported A bloom of phototrophic bacteria in the marine salterns of Salins-de-Giraud, located on the Mediterranean French coast in the Rh one Delta is also described.