Genus III Halochromatium Imhoff SUling and Petri 1998b 1139VP

Johannes F. Imhoff and Pierre Caumette

Ha'' Gr. gen. n. halos of the salt; Chromatium a genus name; M.L. neut. n. Halochromatium the Chromatium of the salt.

Cells straight to slightly curved rods, single or in pairs, multiply by binary fission. Motile by polar flagella, Gram negative, belong to the Gammaproteobacteria, and contain internal photosynthetic membranes of vesicular type with bacteriochlorophyll a and ca-rotenoids as photosynthetic pigments.

Photolithoautotrophic growth under anoxic conditions in the light with sulfide and S0 as electron donor. During oxidation of sulfide, S0 is formed as an intermediate and stored in the form of highly refractile globules inside the cells. Sulfate is the final oxidation product. Hydrogen may be used as electron donor. In the presence of sulfide and bicarbonate, organic substrates can be photoassimilated. Chemolithotrophic and chemoorgano-trophic growth under microoxic conditions in the dark is possible.

Mesophilic bacteria with optimum growth at 20-35°C, and pH 7.2-7.6. Elevated salt concentrations are required for growth.

Habitat: Reduced sediments in salinas, microbial mats in hypersaline environments, and coastal lagoons with elevated salt concentrations, which are exposed to the light.

Type species : Halochromatium salexigens (Caumette, Baulaigue and Matheron 1988) Imhoff, Siiling and Petri 1998b, 1140 (Chromatium salexigens Caumette, Baulaigue and Matheron 1988, 291.)

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