Bacteria arsenate respiration

L.L., Lisak, J., Stolz, J.F., Oremland, R.S. (2002). Dissimila-tory arsenate reductase activity and arsenate-respiring bacteria in bovine rumen fluid, hamster feces, and the termite hindgut. FEMS Microbiol. Ecol. 41 59-67. 

High arsenic concentrations can also occur in alkaline, closed-basin lakes. Mono Lake, California, USA has dissolved arsenic concentrations of (10-20) X lO pg with pH values in the range 9.5-10 as a result of the combined influences of geothermal activity, weathering of mineralized volcanic rocks, evaporation of water at the lake surface, and a thriving population of arsenate-respiring bacteria (Maest et al., 1992 Oremland et al., 2000). 

Figure 8 Predicted contributions, based on comparison of rates, for biological and sulfide reduction of arsenate in (a) pure cultures of arsenate respiring bacteria and (b) for natural settings. (Rate data for biological reduction by strain SES3 are from Ref. 54, and for sediments from Ref. 69 data from Refs. 56 and 68 used to calculate sulfide reduction rates.)...

Most of the above examples followed the dissolution of arsenic in complex sediment systems amended with scorodite and cultures of iron- or arsenate-respiring bacteria. More work was needed with simpler, defined systems to unravel the biological mechanisms from the adsorptive chemical phenomena. Zobrist et al. (43) studied the reductive dissolution of ferrihydrite that was coprecipitated with arsenate. Sulfurospirillum barnesii was the organism of choice because it respires both Fe(III) and As(V). Washed cell suspensions of S. barnesii simultaneously reduced Fe(III) as well as As(V) (Fig. 9). However, As(III) still had a... 

These experiments pointed out that respiratory reduction of As(V) sorbed to solid phases can indeed occur in nature, but its extent and the degree of mobilization of the As(III) product is constrained by the type of minerals present in a given system. What remains unclear is whether micro-organisms can actually reduce As(V) while it is attached to the mineral surface, or if they attack a mono-layer of aqueous As(V) that is in equilibrium with the As(V) adsorbed onto the surface layer. If, as is the case for dissimilatory metal-reducing bacteria such as Geobacter sulfurreducens and Shewanella oneidensis (44,45), components of the electron transport chain are localized to the outer-membrane of some arsenate-respiring bacteria, direct reductive dissolution of insoluble arsenate minerals may be possible by attached bacteria. Too little is known at present about the topology... 

Anoxic water samples, because they contain little in the way of particles, are far easier than aquifer materials to develop radioassays for the measurement of arsenate reduction. Arsenic speciation quantitatively changes from arsenate to arsenite with vertical transition from the surface oxic waters to the anoxic bottom depths of stratified lakes and fjords (55,56). This also occurs in Mono Lake, California (57), a transiently meromictic, alkaline (pH = 9.8), and hypersaline (salinity = 70-90 g/L) soda lake located in eastern California (Fig. 11). The combined effects of hydrothermal sources coupled with evaporative concentration have resulted in exceptionally high ( 200 fiM) dissolved arsenate concentrations in its surface waters. Haloalkaliphilic arsenate-respiring bacteria have been isolated from the lake sediments (26), and sulfate reduction, achieved with... 

The reduction of arsenate [As(V)] to arsenite [As(III)] is known to occur in anoxic environments (1,2). Until recently, however, the organisms responsible for this reduction were not known. A number of different bacteria have been isolated that are able to respire with arsenate, reducing it to arsenite. With one exception, these organisms use the nonrespiratory substrate lactate as the electron donor (3-6) and are listed in Table 1. Two of them, Desulfotomaculum auripig-mentum str. OREX-4 (7,8) md Desulfomicrobium sp. str. Ben-RB (9), also respire with sulfate as the terminal electron acceptor. None are able to use the respiratory substrate acetate as the electron donor for arsenate respiration. The only organism known able to do so is Chrysiogenes arsenatis (10). 

Phylogenetically, C. arsenatis differs from the other arsenate-respiring bacteria and from other phyla of the Bacteria and so is the first representative of a new phylum (11) (see Table 1). The other arsenate-respiring bacteria fall within three different divisions of the Bacteria (see Table 1). The two Bacillus species are, however, unrelated to D. auripigmentum even though they are all members of the low G + C gram-positive bacteria. 

Desorption on Metal Reduction Many bacteria and archaea can respire on Mn(lll/tV) and Fe(lll) oxides, leading to their dissolution, with the potential for concomitant displacement of arsenic into the aqueous phase (Cummings et al., 1999). In fact, within most soils and sediments, total As levels correlate with Fe content rather than Al or clay content (Smedley and Kinniburgh, 2002), and thus reductive dissolution—transformation of Fe(lll) phases should have a major impact on arsenic. Respiratory reduction of Fe in sediments generally occurs in zones where O2, NOs , and Mn(lV) [all being oxidants of Fe(ll) and alternative electron acceptors] are diminished (Lovley, 2000). 

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). 

Table 2 Approximate Time Scales of Microbiologically Mediated Reduction of Arsenate to Arsenite Performed by Bacteria Capable of Utilizing As(V) as a Terminal Electron Acceptor During Anaerobic Respiration (Dissimilatory Reduction) or by Organisms Either Containing, or Presumed to Contain, ars Genes that Code for an Arsenate Reductase and an Arsenite Efflux Pump...

Two new organisms that respire anaerobically using arsenate as the terminal electron acceptor have been isolated from arsenic-contaminated areas in Victoria, Australia. One of these organisms, C. arsenatis, is the first representative of a new phylum of the Bacteria and uses the respiratory substrate acetate as the elec-... 

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