Taxonomic Comments

Species of this genus have previously been classified as belonging to the genus Chromatium (Pfennig and Triiper, 1974; Pfennig, 1989b). However, because of significant phenotypic and genetic differences to true Chromatium species and other members of the family Chromatiaceae, they have been transferred to the new genus Marichromatium (Imhoff et al., 1998b).

Further Reading

Imhoff, J.F., Silling, J. and Petri, R. 1998. Phylogenetic relationships among the Chromatiaceae, their taxonomic reclassification and description of the new genera Allochromatium, Halochromatium, Isochro-matium, Marichromatium, Thiococcus, Thiohalocapsa, and Thermochro-matium. Int. J. Syst. Bacteriol. 48: 1129-1143.

Marichromatium species can be distinguished on the basis of cell suspension color and pigment content, differences in substrate utilization, as well as slight differences in cell size and salt response. Characteristic properties for distinguishing Marichroma-tium species are shown in Table BXII.y.5 of the chapter describ ing the family Chromatiaceae. The phylogenetic relationships of Marichromatium species to other members of the family Chroma-tiaceae is shown in Fig. BXII.y.3 of the chapter describing the family Chromatiaceae.

List of species of the genus Marichromatium

1. Marichromatium gracile (Strzeszewski 1913) Imhoff, Suling gra' ci.le. L. neut. adj. gracile thin, slender.

and Petri 1998b, 1140VP (Chromatium gracile Strzeszewski 1913, 321.)

Cells are rod shaped, 1.0-1.3 X 2-6 |m. Globules of S0 evenly distributed within cells. Single cells colorless. Color of growing cultures orange-brown to brownish red. Photosynthetic pigments are bacteriochlorophyll a and carot-enoids of the normal spirilloxanthin group.

Photolithoautotrophic growth under anoxic conditions in the light with sulfide, sulfur, thiosulfate, sulfite, and molecular hydrogen as electron donors. Organic substrates formate, acetate, propionate, pyruvate, fumarate, malate, succinate, lactate, propionate, butyrate, crotonate, and Casa-mino acids are used. Not utilized: sugars, sugar alcohols, alcohols, benzoate, citrate, and amino acids. Chemoauto-trophic and mixotrophic growth under microoxic to semi-oxic conditions possible. Assimilatory sulfate reduction occurs (Thiele, 1968). Nitrogen sources: ammonium salts, N2. Vitamins not required.

Habitat: brackish waters, estuaries, salt marshes, and marine habitats containing hydrogen sulfide and exposed to the light.

Mesophilic, marine bacterium with optimum growth at 2-3% NaCl, pH 7.2-7.4 (range 6.8-7.6), and a temperature range of 20-35°C.

The mol% G + C of the DNA is: 68.9-70.4 (Bd); type strain 69.9 (Bd).

Type strain: 8611, BN 5210, DSM 203.

GenBank accession number (16S rRNA): X93473.

2. Marichromatium purpuratum (Imhoff and Trüper 1980) Imhoff, Suling and Petri 1998b, 1140VP (Chromatium purpuratum Imhoff and Trüper 1980, 69.)

purpura'tum. L. neut. adj. purpuratum dressed in purple.

Cells are rod shaped, 1.2-1.7 X 3-4 |m, when grown under autotrophic conditions, motile by a single polar fla-gellum. Color of cell suspensions purple-red. Photosyn-thetic pigments are bacteriochlorophyll a and carotenoids of the okenone group.

Obligately phototrophic and strictly anaerobic. Photo-lithoautotrophic growth with sulfide, sulfur, and thiosulfate as electron donors; photoorganoheterotrophic growth with acetate, propionate, butyrate, valerate, lactate, pyruvate, fu-marate, malate, and succinate in the presence of bicarbonate. Fructose and casamino acids are poor substrates. Not utilized: sugars, sugar-alcohols, alcohols, higher fatty acids, benzoate, and amino acids. Nitrogen sources: ammonium salts. Vitamins not required.

Mesophilic marine bacterium that requires NaCl for growth, optimum salinity 5% NaCl, salinity range 2-7% NaCl, pH range 7.2-7.6, temperature range 25-30°C.

Habitat: anoxic and sulfidic marine sediments and waters exposed to the light, marine sponges, and other marine invertebrates, such as didemnids and copepods.

Type strain: BN 5500, DSM 1591.

GenBank accession number (16S rRNA): AF001580, AJ224439.

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