Isolation, Growth, and Metabolism of an Obligately Anaerobic, Selenate-Respiring Bacterium, Strain SES-3

Abstract

A gram-negative, strictly anaerobic, motile vibrio was isolated from a selenate-respiring enrichment culture. The isolate, designated strain SES-3, grew by coupling the oxidation of lactate to acetate plus CO2 with the concomitant reduction of selenate to selenite or of nitrate to ammonium. No growth was observed on sulfate or selenite, but cell suspensions readily reduced selenite to elemental selenium (Seo). Hence, SES-3 can carry out a complete reduction of selenate to Seo. Washed cell suspensions of selenate-grown cells did not reduce nitrate, and nitrate-grown cells did not reduce selenate, indicating that these reductions are achieved by separate inducible enzyme systems. However, both nitrate-grown and selenate-grown cells have a constitutive ability to reduce selenite or nitrite. The oxidation of ['4C] lactate to '4Co2 coupled to the reduction of selenate or nitrate by cell suspensions was inhibited by CCCP (carbonyl cyanide m-chlorophenylhydrazone), cyanide, and azide. High concentrations of selenite (5 mM) were readily reduced to Seo by selenate-grown cells, but selenite appeared to block the synthesis of pyruvate dehydrogenase. Tracer experiments with [75Se] selenite indicated that cell suspensions could achieve a rapid and quantitative reduction of selenite to Seo. This reduction was totally inhibited by sulfite, partially inhibited by selenate or nitrite, but unaffected by sulfate or nitrate. Cell suspensions could reduce thiosulfate, but not sulfite, to sulfide. These results suggest that reduction of selenite to Seo may proceed, in part, by some of the components of a dissimilatory system for sulfur

REDUCTION OF SELENIUM OXYANIONS BY ENTEROBACTER CLOACAE STRAIN SLD1a-1: REDUCTION OF SELENATE TO SELENITE

“…The influence of alternate electron acceptors on reduction of and on growth was variable ( Table 1). Respiration 2Ϫ SeO 4 has been identified as a mechanism by which bacteria reduce Se oxyanions [19,25,26]. As noted, previous work in our laboratory with SLD1a-1 has shown that reduction of oc-2Ϫ SeO 4 curs via terminal reductase(s) as a result of respiration [9].…”

Transformations of selenate and selenite by Stenotrophomonas maltophilia isolated from a seleniferous agricultural drainage pond sediment

“…In the case of S. maltophilia, NO 3 should not interfere with the reduction of either Se oxyanion since the organism cannot respire NO 3 -(data not shown), but additional studies are scheduled to determine if the organism displays a negative physiological response to high NO 3 concentrations. Of additional importance, S. maltophilia can reduce SeO 4 2and SeO 3 2under microaerophilic conditions; in contrast, the majority of work on Se-reducing bacteria has focused on organisms that require strict anaerobicity (Gerhardt et al, 1991;Tomei et al, 1992;Macy, 1994;Oremland et al, 1994;Rege et al, 1999). Because bioreactor influent will contain O 2 , the ability of S. maltophilia to grow in the presence of O 2 and rapidly reduce Se oxyanions in the presence of low levels of O 2 could be extremely advantageous.…”

Factors affecting soluble selenium removal by a selenate-reducing bacterium Bacillus sp. SF-1

“…Recently, some bacterial strains which can effectively reduce selenate into selenite or elemental selenium have been reported [2,[6][7][8]12]. They are all gram-negative bacteria.…”

“…During the selenate-and selenite-reduction, cell growth was observed. Like Thauera selenatis [5,6] and Sulufurospirillum barnesii strain SES-3 [3,4,12], SF-1 grew with selenate or selenite as an electron acceptor and lactate as an electron donor for the anaerobic respiration.…”