An arsenate-reducing and alkane-metabolizing novel bacterium, Rhizobium arsenicireducens sp. nov., isolated from arsenic-rich groundwater.

A novel arsenic (As)-resistant, arsenate-respiring, alkane-metabolizing bacterium KAs 5-22, isolated from As-rich groundwater of West Bengal was characterized by physiological and genomic properties. Cells of strain KAs 5-22 were Gram-stain-negative, rod-shaped, motile, and facultative anaerobic. Growth occurred at optimum of pH 6.0-7.0, temperature 30 °C. 16S rRNA gene affiliated the strain KAs 5-22 to the genus Rhizobium showing maximum similarity (98.4 %) with the type strain of Rhizobium naphthalenivorans TSY03b followed by (98.0 % similarity) Rhizobium selenitireducens B1. The genomic G + C content was 59.4 mol%, and DNA-DNA relatedness with its closest phylogenetic neighbors was 50.2 %. Chemotaxonomy indicated UQ-10 as the major quinone; phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol as major polar lipids; C, C, 2-OH C, 3-OH C, and unresolved C ɷ7C/ɷ9C as predominant fatty acids. The cells were found to reduce O, As, NO, SO and Fe as alternate electron acceptors. The strain's ability to metabolize dodecane or other alkanes as sole carbon source using As as terminal electron acceptor was supported by the presence of genes encoding benzyl succinate synthase (bssA like) and molybdopterin-binding site (mopB) of As respiratory reductase (arrA). Differential phenotypic, chemotaxonomic, genotypic as well as physiological properties revealed that the strain KAs 5-22 is separated from its nearest recognized Rhizobium species. On the basis of the data presented, strain KAs 5-22 is considered to represent a novel species of the genus Rhizobium, for which the name Rhizobium arsenicireducens sp. nov. is proposed as type strain (=LMG 28795=MTCC 12115).