Submitted to: Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/29/2002
Publication Date: 4/1/2003
Citation: DUNGAN, R.S., YATES, S.R., FRANKENBERGER, W.T. TRANSFORMATIONS OF SELENATE AND SELENITE BY STENOTROPHOMONAS MALTOPHILIA ISOLATED FROM A SELENIFEROUS AGRICULTURAL DRAINAGE POND SEDIMENT. ENVIRONMENTAL MICROBIOLOGY. 2003. Interpretive Summary: At the western side of California's San Joaquin Valley, agricultural irrigation waters leach naturally elevated levels of selenium (Se) from soil. The drainage waters are then disposed of in evaporation ponds, where Se accumulates to toxic levels in the sediment and water. Although Se is an essential micronutrient for humans and animals, at excessive concentrations in the environment, Se bioaccumulates in the food chain and is a serious threat to wildlife. The most notable case in California was observed in Kesterson Reservoir, where severe Se contamination was linked to embryonic deformities of aquatic birds, which ultimately led to the closure of the Reservoir in 1985. This has led to considerable interest in the microbiological transformation of Se oxyanions to volatile and insoluble forms of Se. Biotransformation mechanisms are potentially useful for reducing in situ Se contamination in agricultural sediments and wastewaters. In this study, a strain of Stenotrophomonas maltophilia has been isolated and is currently being studied for its potential for bioremediation. The organism is capable of rapidly transform Se oxyanions, S. maltophilia may be useful in a low-cost remediation scheme (e.g., bioreactor or in situ process) designed to treat seleniferous agricultural wastewater. The method has the potenital for treatment of Se-contaminated agricultural drainage waters, at a low cost compared to other methods.
Technical Abstract: A Gram-negative bacterium, identified as Stenotrophomonas maltophilia by fatty acid analysis and 16S rRNA sequencing, was isolated from a seleniferous agricultural evaporation pond sediment collected in the Tulare Lake Drainage District, California. In cultures exposed to the atmosphere, the organism reduces selenate and selenite to red amorphous elemental selenium only upon reaching stationary phase, when oxygen levels are less than 0.1 mg/L. In 48 h, S. maltophilia removed 81.2 percent and 99.8 percent of added SeO42' and SeO32' (initial concentration of 0.5 mM), respectively, from solution. Anaerobic growth experiments revealed that the organism was incapable of using SeO42', SeO32', SO42'or NO3'as a terminal electron acceptor. Transmission electron microscopy of cultures spiked with either Se oxyanion were found to contain spherical extracellular deposits. Analysis of the deposits by energy dispersive X-ray spectroscopy revealed that they consist of Se. Furthermore, S. maltophilia was active in producing volatile alkylselenides when in the presence of SeO42' and SeO32'. The volatile products were positively identified as dimethyl selenide (DMSe), dimethyl selenenyl sulphide (DMSeS) and dimethyl diselenide (DMDSe) by gas chromatography-mass spectrometry. Our findings suggest that this bacterium may contribute to the biogeochemical cycling of Se in seleniferous evaporation pond sediments and waters. This organism may also be potentially useful in a bioremediation scheme designed to treat seleniferous agricultural wastewater.