Phaeospirillum oryzae sp. nov., a spheroplast-forming, phototrophic alphaproteobacterium from a paddy soil

Abstract

Two strains (JA317T and JA559) of spiral shaped, spheroplast-forming, anaerobic, Gram-negative, motile purple non-sulfur bacteria were isolated from rhizosphere soils of paddy and were characterized by a polyphasic taxonomic approach. Bacteriochlorophyll a and carotenoids, rhodopin, lycopene and rhodopin glucoside, were present as photosynthetic pigments. Intracellular photosynthetic membranes were of stacked type. The major fatty acids were C18 : 1ω7c, C16 : 0 and C16 : 1ω6c/C16 : 1ω7c in both strains. The genomic DNA G+C content was 63.3±0.8 mol%. The two strains were closely related (mean DNA–DNA hybridization >85 %). Phylogenetic analysis showed that the strains clustered with the species of the genus Phaeospirillum, which belongs to the family Rhodospirillaceae within the class Alphaproteobacteria. Based on 16S rRNA gene sequence analysis, strains JA317T and JA559 showed highest sequence similarity with the type strains of Phaeospirillum chandramohanii (98.2 %), Phaeospirillum molischianum (97.4 %) and Phaeospirillum fulvum (97.1 %) of the family Rhodospirillaceae. Strain JA317T can be clearly distinguished from P. chandramohanii with respect to spheroplast formation and several other morphological and physiological properties. DNA–DNA relatedness of strain JA317T with its closest relatives of the genus Phaeospirillum was less than 55 %. It is evident from the phenotypic, chemotaxonomic and molecular genetic evidence that strain JA317T represents a novel species of the genus Phaeospirillum, for which the name Phaeospirillum oryzae sp. nov., is proposed. The type strain of the species is JA317T ( = NBRC 104938T  = KCTC 5704T).