Phaeobacterium nitratireducens gen. nov., sp. nov., a phototrophic gammaproteobacterium isolated from a mangrove forest sediment sample

Abstract

A novel brown-coloured, Gram-negative-staining, rod-shaped, motile, phototrophic, purple sulfur bacterium, designated strain AK40^T , was isolated in pure culture from a sediment sample collected from Coringa mangrove forest, India. Strain AK40^T contained bacteriochlorophyll a and carotenoids of the rhodopin series as major photosynthetic pigments. Strain AK40^T was able to grow photoheterotrophically and could utilize a number of organic substrates. It was unable to grow photoautotrophically and did not utilize sulfide or thiosulfate as electron donors. Thiamine and riboflavin were required for growth. The dominant fatty acids were C_{12 : 0}, C_{16 : 0}, C_{18 : 1}v7c and summed feature 3 (C16 : 1v7c and/or iso-C_{15 : 0} 2-OH). The polar lipid profile of strain AK40^T was found to contain diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and eight unidentified lipids. Q-10 was the predominant respiratory quinone. The DNA G+C content of strain AK40^T was 65.5 mol%. 16S rRNA gene sequence comparisons indicated that the isolate represented a member of the family Chromatiaceae within the class Gammaproteobacteria. 16S rRNA gene sequence analysis indicated that strain AK40^T was closely related to Phaeochromatium fluminis, with 95.2 % pairwise sequence similarity to the type strain; sequence similarity to strains of other species of the family was 90.8–94.8 %. Based on the sequence comparison data, strain AK40^T was positioned distinctly outside the group formed by the genera Phaeochromatium, Marichromatium, Halochromatium, Thiohalocapsa, Rhabdochromatium and Thiorhodovibrio. Distinct morphological, physiological and genotypic differences from previously described taxa supported the classification of this isolate as a representative of a novel species in a new genus, for which the name Phaeobacterium nitratireducens gen. nov., sp. nov. is proposed. The type strain of Phaeobacterium nitratireducens is AK40^T (5JCM 19219^T 5MTCC 11824^T )