Chapter 9 : Dissimilatory Reduction of Selenate and Arsenate in Nature

Dissolved selenate, selenite, sulfate, and chloride in the porewaters of sediments from an agricultural wastewater evaporation pond located in the San Joaquin Valley, Calif. Reprinted from reference 55 with permission of the American Society for Microbiology.

Chemical gradients in Mono Lake during a period of meromixis in the 1980s. Reprinted from reference 40 , with permission of the publisher.

Arsenate reduction in estuarine sediments incubated under an atmosphere of nitrogen (A), hydrogen (B), air (C), or nitrogen with autoclaved sediments (D). Symbols: o As(V); ●, As(III). Reprinted from reference 12 with permission of the American Society for Microbiology.

Reduction of 75Se(VI) by sediments from Hunter Drain located in western Nevada. Counts in pellet indicate the formation of 75Se(0). Sediments were incubated at ambient Se(VI) concentrations of ∼0.5 μM with no additions or with addition of 17 μM unlabeled Se(VI) or were heat killed and incubated with ambient levels of Se(VI). Reprinted from reference 54 with permission of the publisher.

(A) Reduction of 75Se(VI) to solid 75Se(V) by sediments taken from Massie Slough in western Nevada. (B) Recovery of counts into various solvent fractions. Reprinted from reference 67 with permission of the American Society for Microbiology.

Michaelis-Menten kinetics displayed by selenate reduction in sediments from Massie Slough. Reprinted from reference 67 with permission of the American Society for Microbiology.

Metabolism of [2-l4C]acetate to 14CH4 and 14CO2 by estuarine sediments incubated with 10 mM sulfate, with sulfate plus 1, 10, or 20 mM molybdate, or with sulfate plus 1, 10, or 20 mM selenate. Reprinted from reference 55 with permission of the American Society for Microbiology.

Metabolism of [2-14C]acetate to 14CH4 and 14CO2 by anoxic sediments from salt marsh (A) or freshwater lake (B) sources in the presence of different concentrations of arsenate. Reprinted from reference 12 with permission of the American Society for Microbiology.

Selenate reduction activity in depth profiles taken from three sites in western Nevada: (A) South Lead Lake; (B) Hunter Drain; and (C) Massie Slough. Symbols: ●·, 0 to 5 cm; o, 5 to 10 cm; ■, 10 to 15 cm. Reprinted from reference 53 with permission of the American Society for Microbiology.

Electron micrographs of the selenium-reducing bacteria S. barnesii strain SES-3 (A and B), strain E-1H from Mono Lake (C and D), and strain MLS-10 from Mono Lake (E and F). (A, C, and E) Scanning electron microscopy by J. Switzer Blum, A. Burns, and R. S. Oremland (unpublished). (B. D, and F) Transmission electron microscopy by J. F. Stolz. Bars, 0.5 μm. Extracellular ball-like particles in panel E are elemental selenium as determined from X-ray energy-dispersive spectrometry done in association with the scanning electron microscopy.

Phylogenic trees based on 16S rRNA sequence data using maximum-parsimony analysis of the gram-positive arsenate- and selenate-reducing bacterium E1-H (A) and the gram-negative arsenate- and selenate-reducing bacterium S. barnesii strain SES-3 and the arsenate-reducing bacterium S. arsenophilus strain MIT-13 (B).

Growth of S. barnesii strain SES-3 with Se(VI) as the electron acceptor. Reprinted from reference 52 with permission of the American Society for Microbiology.

Growth of strain E-IH in Mono Lake water with Se(VI) as the electron acceptor. From J. Switzer Blum, A. Burns Bindi, and R. S. Oremland, unpublished data.

Growth of strain MLS-10 in Mono Lake water with Se(IV) as the electron acceptor. From J. Switzer Blum, A. Burns Bindi, and R. S. Oremland, unpublished data.

Growth of S. barnesii strain SES-3 with As(V) as the electron acceptor. Reprinted from reference 28 with permission of the American Society for Microbiology.