Phaeovibrio sulfidiphilus gen. nov., sp. nov., phototrophic alphaproteobacteria isolated from brackish water

Two strains (JA480(T) and JA481) of phototrophic alphaproteobacteria were isolated from sediment samples collected from brackish water near Nagapattinam, India. They were Gram-negative, vibrioid cells containing bacteriochlorophyll a and rhodopin as major photosynthetic pigments. Most cells of both strains were non-flagellated; 1 % of cells showed two monopolar flagella. Cells showed positive phototaxis. Both strains showed chimeric intracellular photosynthetic membranes, where both lamellar stacks and vesicles were present together in a single cell. The major fatty acids were C(18 : 1)ω7c and C(16 : 0) in both strains. The genomic G+C content was 67.2-68.8 mol% and the two strains were closely related (mean DNA-DNA hybridization >85 %). 16S rRNA gene sequence comparisons indicated that the isolates represent members of the Rhodospirillaceae within the class Alphaproteobacteria. According to the sequence comparison data, strain JA480(T) is positioned distinctly outside the group formed by the phototrophic genera Rhodospirillum, Rhodocista, Phaeospirillum, Rhodovibrio, Rhodospira and Roseospira, with only 80-92 % 16S rRNA gene sequence similarity. Distinct morphological, physiological and genotypic differences from previously described taxa support the classification of this isolate as a representative of a novel species in a new genus, for which the name Phaeovibrio sulfidiphilus gen. nov., sp. nov. is proposed. The type strain of Phaeovibrio sulfidiphilus is JA480(T) ( = KCTC 5825(T) = NBRC 106163(T) = DSM 23193(T)).