Phaeospirillum tilakii sp. nov., a phototrophic alphaproteobacterium isolated from aquatic sediments.

Two strains (JA492(T) and JA590) of spiral-shaped, anaerobic, Gram-stain-negative, motile, purple non-sulfur bacteria were isolated from aquatic sediments from a bird sanctuary and a stream, respectively, and were characterized by a polyphasic taxonomic approach. Bacteriochlorophyll a and carotenoids (rhodopin, lycopene, hydroxylycopene glucoside and dihydroxylycopene diglucoside) were present as photosynthetic pigments. Intracellular photosynthetic membranes were of the stacked type. The major fatty acids were C(18 : 1)ω7c, C(16 : 0) and summed feature 3 (C(16 : 1)ω6c and/or C(16 : 1)ω7c) in both strains. Ubiquinones and menaquinones were present as major quinone components. The genomic DNA G+C contents of strains JA492(T) and JA590 were 63.8 and 61.5 mol%, respectively. Both strains were closely related (mean DNA-DNA hybridization >70 %). Phylogenetic analysis showed that the strains clustered with species of the genus Phaeospirillum of the family Rhodospirillaceae, class Alphaproteobacteria. Based on 16S rRNA gene sequence analysis, both strains showed highest sequence similarity with Phaeospirillum oryzae JA317(T) (97.2-97.4 %), Phaeospirillum molischianum DSM 120(T) (96.5-96.7 %), Phaeospirillum fulvum DSM 113(T) (96.7-96.9 %) and Phaeospirillum chandramohanii JA145(T) (96.5-96.7 %). DNA-DNA relatedness between strain JA492(T) and its closest relative in the genus Phaeospirillum was less than 42 %. It is evident from phenotypic, chemotaxonomic and molecular genetic data that strain JA492(T) represents a novel species of the genus Phaeospirillum, for which the name Phaeospirillum tilakii sp. nov. is proposed; the type strain is JA492(T) ( = NBRC 107650(T) = KCTC 15012(T)).