Taxonomic Comments

The genus name Thiococcus was proposed for this bacterium by Eimhjellen et al. (1967). However, this name was never validly published and later the bacterium was validly named Thiocapsa pfennigii (Eimhjellen, 1970; Approved List of Bacterial Names, Skerman et al., 1980). Because of the striking genetic and phe-notypic difference between Thiococcus pfennigii and members of the genus Thiocapsa, it was transferred to a new genus and the name Thiococcus was revived (Imhoff et al., 1998b). A possible candidate for the neotype strain of Thiococcus pfennigii (strain DSM 226, Truper 8013, Imhoff 4250) belongs to the cluster of truly marine species of the family Chromatiaceae (Fig. BXII.y.3 of the chapter describing the family Chromatiaceae) and requires at least 1% NaCl for growth. The salt dependence and natural distribution of this species are poorly understood. The original type strain was isolated from a freshwater source (river water), but unfortunately was lost. Additional strains were isolated later from freshwater and marine sources. However, chemotaxonomic and genetic analyses have not been performed on these strains. In addition, salt dependence has not yet been determined for all of the isolates.

Further Reading

Eimhjellen, K.E 1970. Thiocapsa pfennigii sp. nov., a new species of pho-

totrophic sulfur bacteria. Arch. Microbiol. 73: 193-194. Eimhjellen, K.E., Steensland, H. and Traetteberg, H. 1967. A Thiococcus sp. nov. gen., its pigments and internal membrane system. Arch. Mi-crobiol. 59: 82-92. Imhoff, J.F., Suling, 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.

List of species of the genus Thiococcus

1. Thiococcus pfennigii (Eimhjellen 1970) Imhoff, Suling and Petri 1998b, 1139VP (Thiocapsa pfennigii Eimhjellen 1970, 193.)

pfennigi.i. M.L. gen. n. pfennigii of Pfennig, named after N. Pfennig, a German microbiologist.

Cells spherical, 1.2—1.5 |im in diameter; diplococcus-shaped division stages about 2.5 |m long; stationary phase cells 0.8-1.0 |m in diameter. Internal photosynthetic membranes are bundles of ribbon-like branched tubes continuous with the cytoplasmic membrane. Individual cells colorless, color of cell suspensions yellowish to orange-brown. Photosynthetic pigments are bacteriochlorophyll b and the carotenoid 3,4,3',4'-tetrahydrospirilloxanthin (Eimhjellen et al., 1967).

Obligately phototrophic and strictly anaerobic. Photo-

lithoautotrophic growth with sulfide and S0 as electron donors. In the presence of sulfide and bicarbonate, acetate, pyruvate, propionate, lactate, fumarate, succinate, malate, and fructose are photoassimilated. Not utilized: thiosulfate and butyrate. Nitrogen sources: ammonium salts and N2.

Mesophilic bacterium with optimum growth at 0.5-2% NaCl, 20-35°C, and pH 7.0 (range 6.5-7.5).

Habitat: freshwater, brackish, and marine waters and sediments with hydrogen sulfide and exposed to the light.

Type strain: DSM 1375 (RG3, Nidelven) is lost; no neotype strain is designated.

GenBank accession number (16S rRNA): Y12373 (strain DSM 226).

Additional Remarks: The GenBank accession number for strain BN 4254 (Pfennig 8320) is AJ010125.

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