Description of New Strains and Features of the Ultra-Fine Structure of Cells of the Purple Sulfur Bacteria Thiorhodospira sibirica

The properties of four strains of the alkaliphilic halotolerant purple sulfur bacterium Thiorhodospira sibirica isolated from steppe soda lakes (mineralization 7–35 g/l, pH 9.0–9.8) located in the Zabaikalsky Krai and the Republic of Buryatia (Russia) and northeastern Mongolia were studied. All the studied strains had morpho-physiological properties characteristic of Trs. sibirica: a unique spectrum of pigment absorption in vivo, having four absorption maxima of bacteriochlorophyll a in the near infrared region and unusually located photosynthetic membranes of the lamellar type. Bacteria of all the studied strains, as well as the type strain A12T (= ATCC 700588T), formed elemental sulfur as an intermediate product of sulfide oxidation, the globules of which had an intracellular localization, and not extracellular as in other Ectothiorhodospiraceae. Using the example of the type strain, the intracellular location of the elemental sulfur globules was shown on ultrathin sections using a specific reaction with silver nitrate. All the studied strains had 93–95% similarity according to the results of DNA–DNA hybridization or 98.55–98.61% similarity of the 16S rRNA gene sequences with Trs. sibirica A12T (= ATCC 700588T), which confirms their belonging to the species Trs. sibirica.