Taxonomic Comments

The genus Rhabdochromatium was established by Winogradsky (1888) for long, rod- or spindle-shaped, red sulfur bacteria observed in samples from natural habitats. From microscopic observations of reddish cells containing sulfur globules, he described three species that were distinguished by cell size: Ri. ro-seum, Ri. minus, and Ri. fusiforme. Two more species were described later (see Bavendamm, 1924). Since none of the described species has so far been isolated in pure culture or observed again in samples from nature and enrichment cultures, the genus was not included in the Approved Lists of Bacterial Names. Indeed, this genus was included in the genus Chromatium (Pfennig and Traper, 1974), because long and irregularly swollen cells have been observed in pure cultures of Chromatium okenii, Chromatium weissei, Isochromatium buderi, and Allochromatium warmingii, when the mineral salts concentrations of the culture media were inappropriate. The name Rhabdochromatium was revived, according to Rule 33c of the International Code of Nomenclature of Bacteria (Lapage et al., 1992), for a long, rod-shaped, red sulfur bacterium, the morphology of which has proven to be stable in pure culture for several years. Only one species is currently known. Rhabdochromatium marinum belongs to the cluster of truly marine species of the family Chromatiaceae.

Further Reading

Dilling, W., Liesack, W. and Pfennig, N. 1995. Rhabdochromatium marinum gen. nom. rev., sp. nov., a purple sulfur bacterium from a salt marsh microbial mat. Arch. Microbiol. 164: 125-131.

List of species of the i

1. Rhabdochromatium marinum Dilling, Liesack and Pfennig 1996, 362VP (Effective publication: Dilling, Liesack and Pfennig 1995, 130.)

ma.ri'num. L. neut. adj. marinum marine.

Cells straight rods with slightly conical ends, sometimes slightly bent, 1.5-1.7 X 16-32 |m, motile by a polar tuft of flagella of about 10-20 bipolar fibrils, may be flagellated at both ends. Color of cell suspension beige to orange-brown. Photosynthetic pigments are bacteriochlorophyll a and carotenoids with lycopene as major component.

Obligately phototrophic and strictly anaerobic. Hydrogen, sulfide, S0, and thiosulfate used as electron donors for

Rhabdochromatium photolithoautotrophic growth. In the presence of sulfide and bicarbonate, acetate, propionate, and pyruvate are pho-toassimilated. Growth factors not required.

Mesophilic marine bacterium requiring NaCl for growth: optimum growth at 1.5-5% NaCl, no growth below 1% and above 6.5%, optimum pH 7.2-7.3, optimum temperature 30°C, no growth below 8°C and above 35°C.

Habitat: laminated microbial mat at Great Sippewissett Salt Marsh, Cape Cod, USA.

Type strain: 8315, DSM 5261.

GenBank accession number (16S rRNA): X84316.

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