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Cummings, D.A., 2000

Microbial reduction of iron and selenium in mine spoils

Bibliographic Reference

Cummings, D.A., 2000, Microbial reduction of iron and selenium in mine spoils: University of Idaho, Moscow, Ph.D. dissertation, 216 p.


Two-way interactions between dissimilatory iron-reducing bacteria and their abiotic environment were analyzed in the mining-impacted sediments of Lake Coeur d´Alene, Idaho. Both geochemical and microbiological evidence indicated that microbial Fe(III) reduction was an active and ecologically relevant process in the Lake Coeur d´Alene sediments. Recently reduced (i.e., 0.5 N HCI-soluble) and dissolved ferrous iron was abundant. Iron reducer abundance averaged 105 cells per g, and two new species of the genus Geobacter were isolated and described. Furthermore, DNA analyses indicated that Fe(III)-reducing Geobacteraceae communities changed along a gradient of metals in the Lake Coeur d´Alene sediments: Geobacteraceae species richness and abundance decreased with increasing metals content; community composition changed with changing metals content; and terminal electron-accepting process stratification may have been confounded by the metals load.

The potential for microbial selenium reduction was analyzed in sediments of both Lake Coeur d´Alene and the seleniferous Red Dog Mine tailings impoundment, Alaska. Anaerobic enrichments of Red Dog sediments were capable of elemental selenium precipitation when amended with sodium selenate, hydrogen, and lactate. Enriched bacterial taxa included Acidovorax, Dechlorim onas, Desulfosporosinus, Desulfito bacterium, and Ochrobactrum. Anaerobic selenate-reducing enrichments of Lake Coeur d´Alene, a selenium-poor environment, included Aeromonas and Dechlorisoma spp. We were unable to isolate any anaerobic selenate-reducing bacteria from the selenate-reducing enrichment cultures; however, seven unique aerobic bacteria capable of rapid and extensive selenite reduction to elemental selenium were isolated. These included 5 strains of Bacillus, an Aeromonas sp., and an Ochrobactrum sp. All 7 isolates reduced between 1.5 and 3.6 [mu]M selenite to Se(0) in rich media. The five Bacillus strains expelled Se(0) from the cell by stationary phase, while Aeromonas and Ochrobactrum retained Se(0) within the cell. Furthermore, selenite detoxification suppressed sporulation by the Bacillus isolates. There were no apparent differences in selenite-reducing ability or tolerance of selenate and selenite by strains isolated from the Red Dog and Lake Coeur d´Alene sediments. In addition, standard strains of the isolated taxa were also capable of selenite reduction to Se(0), suggesting that adaptation to high selenium concentrations may not be necessary to maintain selenite-reducing populations in the environment.

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