Rhizobium selenireducens sp. nov.: A selenite reducing a-Proteobacteria isolated from a bioreactor

Authors: Hunter, William; Kuykendall, Larry; Manter, Daniel

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2007
Publication Date: 11/1/2007
Citation: Hunter, W.J., Kuykendall, L.D., Manter, D.K. 2007. Rhizobium selenireducens sp. nov.: A selenite reducing a-Proteobacteria isolated from a bioreactor. Current Microbiology. Vol. 55:455-460.

Interpretive Summary: The paper describes a new species of bacteria that was isolated from a bioreactor that had been used to reduce remove selenate from groundwater. The organism reduces selenite to elemental selenium. Selenite is a natural compound that can be toxic to humans and animals if ingested in amounts that exceed 850 µg Se day -1. There are a number of natural and industrial sources of selenate and selenite and both may be present as contaminants of irrigation or drinking waters. Methods (and organisms) that can remove these compounds from water are needed. Biological approaches, that use microorganisms to remove selenite, offer great promise. For this study we isolated, characterized, and identified a bacterium that removed selenite from water. The organism reduces toxic selenite to elemental red selenium. Reduction effectively removes selenite from the water because elemental selenium is not soluble. Based on rDNA sequence and on fatty acid makeup this bacteria belongs to the bacterial genus Rhizobium but does not belong to any named species within the group. We have proposed that the organism be named Rhizobium selenireducens. The organism may have value as an inoculum for the in situ remediation of groundwater.

Technical Abstract: A Gram-negative, non-pigmented bacterium designated strain B1 was isolated from a laboratory bioreactor that reduced selenate to elemental red selenium (Se0). 16S rRNA gene sequence alignment identified the isolate as a Rhizobium sp. belonging to the Rhizobium clade that includes R. daejeonense, R. giardinii, R. undicola, R. larrymoorei, R. radiobacter, R. rubi, and R. vitis. R. radiobacter and R. rubi are its closest relatives as indicated by 16S rRNA gene sequence alignments which differ from strain B1 by 2.6 and 2.8%, respectively. Within this group strains that show variances that exceed 0.8 to 2.2% have been classified as different species. The major cellular fatty acids present in the B1 strain were C16:0 (1.8%), C18:0 (3.38%), 18:0 3-OH (1.6%), 18:1 '8c (86.8%), 19:0 cyclo'8c (1.5%), and summed features 2 (3.8%) and 3 (1.2%). The large amount of 18:1 '8c present is constant with members of this group of bacteria but the small amounts of 16:0, 19:0 cyclo'8c and summed feature 3 shows variance from R. radiobacter and R. rubi. The strain’s phenotypic and biochemical characteristics were consistent with its placement in this genus.