Differentiation of the genus Thioalkalicoccus from

other genera

According to the results of 16S rDNA sequence analyses (Fig. BXII.y.3) of the chapter describing the family Chromatiaceae, the genus Thioalkalicoccus belongs to the branch of the family Chro-matiaceae that characteristically contains marine and halophilic species. Characteristics for differentiation from other photo-trophic Chromatiaceae species are shown in Table BXII.y.5 of the chapter describing the family Chromatiaceae. Thioalkalicoccus lim-naeus is one of the very few species (in addition to Thiococcus pfennigii and Thioflavicoccus mobilis) that contain tubular internal photosynthetic membranes. The phylogenetic relationships of Thioalkalicoccus species to other members of the family Chroma-tiaceae, based on 16S rDNA sequence comparison, are shown in Fig. BXII.y.3 of the chapter describing the family Chromatiaceae.

List of species of the genus Thioalkalicoccus

1. Thioalkalicoccus limnaeus Bryantseva, Gorlenko, Kompantseva and Imhoff 2000b, 2162VP

lim.nae'us. Gr. fem. n. limne lake, pond, swamp; Gr. adj. limnaios pertaining to, living in lakes, swamps; M.L. masc. adj. limnaeus living in lakes and swamps.

Cells are spherical or oval in shape, multiply by binary fission, and are Gram negative. Internal membranes are of the tubular type. Cells are cocci of 1.3-1.8 |m diameter, usually nonmotile, and surrounded by a thin capsule. Occasionally cells with a single flagellum are observed. Internal photosynthetic membranes of tubular type are formed by invagination of the cell membrane and fill most of the cytoplasm. Color of cell suspensions is yellowish to orange-brown. The absorption spectrum of intact cells exhibits maxima at 410, 462, 492, 530, and 1030 nm, with shoulders at 602 and 835 nm. Photosynthetic pigments are bacterio-chlorophyll b and carotenoids with absorption properties similar to tetrahydrospirilloxanthin.

The metabolism is strictly anaerobic. Photolithoauto-trophic growth occurs in the light with hydrogen sulfide and S0 as electron donors. Thiosulfate was not used for phototrophic growth. During growth with sulfide as electron donor, globules of S0 are accumulated inside the cells. The final oxidation product is sulfate. In the presence of sulfide and sodium bicarbonate, acetate, yeast extract, mal-ate, propionate, pyruvate, succinate, and fumarate were used as organic substrates for phototrophic growth. Growth factors were not required.

Mesophilic, obligate alkaliphilic bacterium with optimum growth at pH 8.8-9.5 (range from 8-10) and 20-25°C. Development is dependent on sodium salts in low concentrations, and good growth occurs over a broad range of salt concentrations without exhibiting a strong optimum, up to 6% NaCl (in the presence of 0.5% sodium carbonates) and up to 8.5% sodium carbonates (in the presence of 0.05% NaCl).

Habitat: Surface of sediments rich in organic matter, and The mol% G + C of the DNA is: 64.0-64.5 (Tm).

microbial mats of soda lakes containing hydrogen sulfide Type strain: A26, ATCC BAA32.

and exposed to the light. GenBank accession number (16S rRNA): AJ277023.

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