Selenium respiration

Oremland, R. S., Blum, J. S., Bindi, A. B., Dowdle, P. R., Herbel, M., and Stolz, J. F. (1999). Simultaneous reduction of nitrate and selenate by cell suspensions of selenium-respiring bacteria. Appl. Environ. Microbiol. 65, 4385-4392. 

Recently, some bacteria have been found which oxidize organic or inorganic compounds with arsenate or selenate (arsenic and selenium respiration) (Stolz and Oremland, 1999). Although many of these bacteria are heterotrophic, Desulfovibrio auripigmentum oxidizes hydrogen with arsenate (and with sulfate, sulfite, thiosulfate, and fumarate). 

Obviously the redox poise in biological systems is very important and the movement of selenium through this process has been investigated for denitrifiers such as Paracoccus denitrificans,159 a specialized selenate-respiring bacterium Thauera selenatis which used selenate as the sole electron acceptor,160,161 and phototrophic bacteria which produced different reduced forms of selenium when amended with either selenite or selenate and even added insoluble elemental Se.162 As noted above, Andreesen has commented on the importance of redox active selenocysteines135 and Jacob et al.136 note the importance of the thioredoxin system to redox poise. 

Aerosol concentrations in excess of 4.0 jag Se/m3 are potentially harmful to human health (Harr 1978). Concentrations in excess of this value (6.0 pg Se/m3) were regularly encountered in the vicinity of the smeltery at Sudbury, Ontario, Canada (Nriagu and Wong 1983). It is not now known whether respiration rates of wildlife, particularly birds, are comparable to those of humans, whether selenium absorption energetics are similar, or whether wildlife species that frequent point sources of air contaminated by high selenium levels for protracted periods are at greater risk than humans. Until additional and more conclusive data become available, aerosol concentrations of less than 4.0 pg Se/m3 are recommended for the protection of sensitive wildlife species. 

Blum JS, Bindi AB, Buzzelli J, Stolz J, Oremland RS (1998) Bacillus arsenicoselenatis, sp. nov., and Bacillus selenitireducens, sp. nov two haloalkaliphiles from Mono Lake, California that respire oxyanions of selenium and arsenic. Arch Microbiol 171 19-30 Brookins DG (1988) Eh-pH Diagrams for Geochemistry. Springer-Verlag, New York... 

Stolz JF, Oremland RS. 1999. Bacterial respiration of arsenic and selenium. FEMS Microbiol Rev 23 615-27. 

There were 37 distinct enzymes that contain molybdenum or tungsten known by the end of 1997. The enzymes are diverse in function, broadly distributed, and include oxidases, reductases, dehydrogenases, a transhydroxylase, and a hydratase. The Mo enzymes are found in eubacteria, archae, protista, fungi, plants, and animals (including humans) and are essential for respiration and carbon and nitrogen assimilation. Several of the enzymatic substrates and products are key components in the nitrogen, sulfur, selenium, carbon, and arsenic cycles and have major biological and environmental impact. 

Small Quantities. Wear nitrile rubber gloves, eye protection, laboratory coat, and respirator (or work in hood). The selenium salt is dissolved in water and the solution is neutralized by the addition of 1 M NaOH (prepared by dissolving 4 g of NaOH in 100 mL of water) or 1 M sulfuric acid (prepared by cautiously adding 5 mL of concentrated acid to 85 mL of cold water). A 1 M solution of sodium sulfide (prepared by dissolving 7.8 g of Na2S in 100 mL of water) is added to the selenium salt solution and the pH is again adjusted to neutral with 1 M sulfuric acid solution. The precipitate is separated by filtration or decantation. Wash, dry, and recycle or send for disposal in a secure landfill.1 ... 

Anaerobic reduction of Se04 and SeO to Se° and methylated selenides Selenate and selenite reduction by microorganisms has been noted for some time. Organisms with this capacity include bacteria and fungi (Trudinger et al., 1979 Stolz Oremland, 1999). In bacteria the reductions are mostly a form of anaerobic respiration and result in selenium immobilization with the formation of water-insoluble Se°. In fungi the reductions involve the formation of methylated selenium,... 

Parris and coworkers applied this technique to the examination of simulated respirant atmospheres that might be found over a culture of microorganisms methylating arsenic, also tin and selenium as trimethylarsine, dimethylselenium and tetramethyltin. 

Biological, chemical, and physical effects of airborne metals are a direct function of particle size, concentration, and composition. The major parameter governing the significance of natural and anthropogenic emissions of environmentally important metals is particle size. Metals associated with fine particulates are of concern particles larger than about 3-fjim aerodynamic equivalent diameter are minimally respirable, are ineffective in atmospheric interactions, and have a short air residence time. Seventeen environmentally important metals are identified arsenic, beryllium, cadmium, chromium, copper, iron, mercury, magnesium, manganese, nickel, lead, antimony, selenium, tin, vanadium, and zinc. This report reviews the major sources of these metals with emphasis on fine particulate emissions. 

Oremland, R. S., Hollibaugh, J. T., Maest, A. S., Presser, T. S., Miller, L. G., and Culbertson, C. W. (1989). Selenate reduction to elemental selenium by anaerobic bacteria in sediments and culture biogeochemical significance of a novel sulfate-independent respiration. Appl. Environ. Microbiol. 55, 2333-2343. 

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