Reduction of Selenite to Elemental Red Selenium by Rhizobium sp. strain B1

Authors: Hunter, William; Kuykendall, Larry

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2007
Publication Date: 10/1/2007
Citation: Hunter, W.J., Kuykendall, L.D. 2007. Reduction of Selenite to Elemental Red Selenium by Rhizobium sp. strain B1. Current Microbiology. Vol. 55: 344-349.

Interpretive Summary: Selenite is a naturally occurring 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 selenite and selenite is a frequent contaminant of irrigation or drinking waters. Methods that can remove excess selenite from water are needed. In situ biological approaches, that use microorganisms to remove selenite, offer great promise and are potentially the most economic approach. For this study we isolated, characterized, and identified a bacterium that removes selenite from water. The mechanism involves the biological reduction of toxic selenite to elemental red selenium. Reduction effectively removes selenium from the water because elemental selenium is not soluble in water and is thus not available for biological uptake. This bacterium, or perhaps its enzymes or DNA, might be useful for the remediation of waters contaminated with Se oxyanions. The organism may have value as an inoculum for the in situ remediation of groundwater. The organism has been identified as a Rhizobium species by morphological and biochemical tests and by 16S rRNA gene sequence alignment.

Technical Abstract: bacterium that reduces the soluble and toxic selenite anion to insoluble elemental red selenium (Se0) was isolated from a laboratory bioreactor. Biochemical, morphological, and 16S rRNA gene sequence alignment identify the isolate as a Rhizobium sp. that is related to but is genetically divergent from R. radiobacter or R. rubi. The isolate was capable of denitrification and reduced selenite to Se0 under aerobic and denitrifying conditions. It did not reduce selenate and did not use selenite or selenate as terminal e- donors. Native gel electrophoresis revealed two bands, corresponding to molecular weights of ~100 and ~45 kD, that reduced selenite. Tungsten inhibited in vivo selenite reduction suggesting that a molybdenum containing protein is involved in selenite reduction. This organism, or its enzymes or DNA, might be useful in bioreactors designed to remove selenite from water.