First genome sequence of a purple sulphur bacterium of the genus Thioalkalicoccus, its characterization as a new isolate of Thioalkalicoccus limnaeus and proposal of strain Um2 as neotype of this species.

Abstract

A new alkaliphilic strain of a purple sulphur bacterium designated as Um2 (=KCTC 25734=VKM B-3893=UQM 41073) with bacteriochlorophyll b and internal photosynthetic membranes of tubular type was isolated from the Umhei hydrothermal system (40 °C, pH 9.3 and salinity 0.42 g l^-1) located in the Baikal rift zone (Russia). Based on morphological and physiological characteristics, this bacterium was classified as Thioalkalicoccus limnaeus. The 16S rRNA gene sequence similarity of strain Um2 was 96.69% with the type strain of Tac. limnaeus A26^T, 95.41% with 'Thioflavicoccus mobilis' 8321^T and 95.34% with Thiococcus pfennigii 4250. The level of similarity of the ribulose 1,5-bisphosphate carboxylase sequences of strain Um2 and known strains of Thioalkalicoccus showed that they belong to the same species. Comparison of the genome nt sequences of strain Um2 revealed that the new isolate was remote from all other described Chromatiaceae species both in digital DNA-DNA hybridization (21.5%) and in average nt identity (76.7%) at the genus level. However, a genome nt sequence had not been determined for any of the known Thioalkalicoccus strains; therefore, the first genome sequence of a member of the genus Thioalkalicoccus is presented here. Tac. limnaeus Um2 is proposed as the neotype, as strain A26^T has been lost from culture collections.