Submitted to: Current Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/19/2005
Publication Date: 4/1/2006
Citation: Hunter, W.J., Kuykendall, L.D. 2006. Identification and characterization of an aeromonas salmonicida achromogenes (syn haemophilus piscium)strain that reduces selenite to elemental red selenium. Current Microbiology 52:305-309. Interpretive Summary: Selenite is a naturally occurring compound that is toxic to both animals and humans when ingested in excess amounts. It is often present in irrigation and drinking waters. Remediation techniques that can remove selenite from contaminated waters are needed and biological approaches that use microorganisms to remove the selenite may prove valuable. We have isolated, characterized, and identified a bacterium that removes selenite from flowing water and that may be useful for the in situ remediation of groundwater. The organism has been identified as Aeromonas salmonicida by morphological and biochemical tests and by 6S rRNA gene sequence alignment. The mechanism involves the biological reduction of the toxic selenite to elemental red selenium. Elemental selenium is not soluble in water and is thus not a groundwater contaminant. The same enzymes that reduce nitrite to nitrous oxide appear to be involved in the process.
Technical Abstract: A bacterium that reduces toxic and mobile selenite to nontoxic and insoluble elemental selenium (Se0) was isolated from a laboratory scale permeable reactive barrier. Biochemical tests and 16S rRNA gene sequence alignment identified the isolate as Aeromonas salmonicida. When incubated on agar plates supplemented with selenite two colony types developed, one more resistant to selenite than the other. Both colony types grew on agar plates containing 16 mM selenite; though colony size (diameter) was reduced to 8% of controls with the small colony type and to 18% with the large colony type. Further study was done with the large colony type. In anaerobic broth culture this bacterium was able to use nitrate as a term electron acceptor but not selenate or selenite. In aerobic culture, when no nitrate was present, early log phase cells removed selenite at a rate of 2.6 ± 0.42 µMoles SeO3-2/mg protein/day. This reduction was retarded by the addition of 25 mM nitrate. Mutants that had a diminished ability to reduce selenite to Se0 also had a reduced ability to reduce nitrate to nitrous oxide. This bacterium, or perhaps its enzymes or DNA, might be useful for the remediation of groundwaters contaminated with selenite. However, care must be exercised because of the pathogenic nature of some Aeromonas species.