Genus VII Marichromatium Imhoff Suling and Petri 1998b 1140VP Johannes F Imhoff

Ma''ti. um. L. gen. n. maris of the sea; Chromatium agenus name; M.L. neut. n. Marichromatium the Chromatium of the sea, the truly marine Chromatium.

Cells straight to slightly curved rods, motile by polar flagella and multiply by binary fission. Cells single or in pairs, and may stick together and form clumps. Gram negative, belong to the Gam-maproteobacteria, and contain internal photosynthetic membranes of vesicular type with bacteriochlorophyll a and carotenoids as photosynthetic pigments.

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

Mesophilic bacteria with optimum growth at 25-35°C, pH 6.57.6, and at salt concentrations typical of marine bacteria.

Habitat: anoxic marine sediments and stagnant waters containing hydrogen sulfide and exposed to the light, marine sponges and other marine invertebrates.

Type species: Marichromatium gracile (Strzeszewski 1913) Imhoff, Süling and Petri 1998b, 1140 ( Chromatium gracile Strzeszewski 1913, 321.)

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