Differentiation of the genus Thiorhodospira from

other genera

Thiorhodospira species may be differentiated from other purple sulfur bacteria by the deposition of S0 both outside and inside the cells, as seen under the light microscope. Differentiation from Ectothiorhodospira and Halorhodospira species is possible on the basis of sulfur deposition both outside and inside the cells, the irregular arrangement of the membrane stacks of photosyn-thetic membranes, the low mol% G + C content, and some characteristic differences in the 16S rDNA sequence (Table BXII.y.7 of the chapter describing the family Ectothiorhodospira-ceae). The 16S rDNA sequence of Thiorhodospira is ~88-92% similar to those of Ectothiorhodospira species. Metabolic properties, such as utilization of carbon, sulfur, and nitrogen sources, are very similar to those of other Ectothiorhodospiraceae. Thiorhodospira species grow at salt concentrations between 0.5-8%, as do Ecto-thiorhodospira species.

List of species of the

1. Thiorhodospira sibirica Bryantseva, Gorlenko, Kompantseva, Imhoff, Suling and Mityushina 1999b, 700VP si.bi'ri.ca. M.L. fem. n. sibirica related or belonging to Siberia.

Cells vibrioid or spirals, 3-4 X 7-20 |im, multiply by binary fission with formation of septa. Motile by means of a monopolar tuft of flagella, which is approximately the same length as the cells. Internal photosynthetic membranes are parallel lamellae piercing the cytoplasm lengthwise or underlying the cytoplasmic membrane. Color of cell suspensions is brownish-red to red. Suspensions of intact cells show absorption maxima at 377, 485, 509, 537-550, 591, 711, 799, 830, 858, and 901 nm. Photosynthetic pig-

1. The basal medium used for isolation and cultivation of Thiorhodospira contains (g/l distilled water): KH2PO4, 0.5 g; NH4Cl, 0.5 g; NaCl, 0.5 g; MgCl2-6H2O, 0.2 g; CaCl2-2H2O, 0.05 g; NaHCO3, 2.5 g; Na2CO3, 2.5 g; Na-acetate, 0.5 g; Na-malate, 0.5 g; yeast extract, 0.1 g; Na^^^O, 0.7 g; and trace element solution SL8, 1 ml. The pH is adjusted to 9.0-9.5 (Bryantseva et al., 1999b).

genus Thiorhodospira ments are bacteriochlorophyll a and carotenoids of the spi-rilloxanthin series, with anhydrorhodovibrin, rhodopin, and spirilloxanthin as major components.

Strictly anaerobic and obligately phototrophic. Photoli-thoautotrophic growth occurs with sulfide and sulfur as electron donors. Thiosulfate is not oxidized. When sulfide and carbonates are present, acetate, pyruvate, malate, suc-cinate, propionate, and fumarate are photoassimilated.

Mesophilic and alkaliphilic brackish-water bacterium with optimum growth at pH 9.0-9.5 (pH-range 7.5-10.5) and 25-30°C. Requires sodium carbonate and/or sodium chloride for growth. Salinity range is 0.5-8% sodium bicarbonate or 0-6% NaCl (in the presence of 0.5% sodium carbonate).

Habitat: Sulfide-containing surface layers of the Lake Malyi Kasytui sediment.

Type strain: A12, ATCC 700588, BN 9312.

GenBank accession number (16S rRNA): AJ006530.

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