Similarities between the Abiotic Reduction of Selenite with Glutathione and the Dissimilatory Reaction Mediated by Rhodospirillum rubrum and Escherichia coli

Various mechanisms have been proposed to explain the biological dissimilatory reduction of selenite (SeO32-) to elemental selenium (Se°), although none is without controversy. Glutathione, the most abundant thiol in the eukaryotic cells, the cyanobacteria, and the α, β, and γ groups of the proteobacteria, has long been suspected to be involved in selenium metabolism. Experiments with the phototrophic α proteobacterium Rhodospirillum rubrum showed that the rate of selenite reduction was decreased when bacteria synthesized lower than normal levels of glutathione, and in Rhodobacter sphaeroides and Escherichia coli the reaction was reported to induce glutathione reductase. In the latter organism superoxide dismutase was also induced in cells grown in the presence of selenite, indicating that superoxide anions (O-2) were produced. These observations led us to investigate the abiotic (chemical) reduction of selenite by glutathione and to compare the features of this reaction with those of the reaction mediated by R. rubrum and E. coli. Our findings imply that selenite was first reduced to selenodiglutathione, which reached its maximum concentration within the 1st min of the reaction. Formation of selenodiglutathione was paralleled by a rapid reduction of cytochrome c, a known oxidant for superoxide anions. Cytochrome c reduction was inhibited by superoxide dismutase, indicating that O-2 was the source of electrons for the reduction. These results demonstrated that superoxide was produced in the abiotic reduction of selenite with glutathione, thus lending support to the hypothesis that glutathione may be involved in the reaction mediated by R. rubrum and E. coli. The second phase of the reaction, which led to the formation of elemental selenium (Se°), developed more slowly. Se° precipitation reached a maximum within 2 h after the beginning of the reaction. Secondary reactions leading to the degradation of the superoxide significantly decreased the yield of Se° in the abiotic reaction compared with that of the bacterially mediated selenite reduction. Abiotically formed selenium particles showed the same characteristic orange-red color, spherical structure, and size as particles produced by R. rubrum, again providing support for the hypothesis that glutathione is involved in the reduction of selenite to elemental selenium in this organism. Various mechanisms have been proposed to explain the biological dissimilatory reduction of selenite (SeO32-) to elemental selenium (Se°), although none is without controversy. Glutathione, the most abundant thiol in the eukaryotic cells, the cyanobacteria, and the α, β, and γ groups of the proteobacteria, has long been suspected to be involved in selenium metabolism. Experiments with the phototrophic α proteobacterium Rhodospirillum rubrum showed that the rate of selenite reduction was decreased when bacteria synthesized lower than normal levels of glutathione, and in Rhodobacter sphaeroides and Escherichia coli the reaction was reported to induce glutathione reductase. In the latter organism superoxide dismutase was also induced in cells grown in the presence of selenite, indicating that superoxide anions (O-2) were produced. These observations led us to investigate the abiotic (chemical) reduction of selenite by glutathione and to compare the features of this reaction with those of the reaction mediated by R. rubrum and E. coli. Our findings imply that selenite was first reduced to selenodiglutathione, which reached its maximum concentration within the 1st min of the reaction. Formation of selenodiglutathione was paralleled by a rapid reduction of cytochrome c, a known oxidant for superoxide anions. Cytochrome c reduction was inhibited by superoxide dismutase, indicating that O-2 was the source of electrons for the reduction. These results demonstrated that superoxide was produced in the abiotic reduction of selenite with glutathione, thus lending support to the hypothesis that glutathione may be involved in the reaction mediated by R. rubrum and E. coli. The second phase of the reaction, which led to the formation of elemental selenium (Se°), developed more slowly. Se° precipitation reached a maximum within 2 h after the beginning of the reaction. Secondary reactions leading to the degradation of the superoxide significantly decreased the yield of Se° in the abiotic reaction compared with that of the bacterially mediated selenite reduction. Abiotically formed selenium particles showed the same characteristic orange-red color, spherical structure, and size as particles produced by R. rubrum, again providing support for the hypothesis that glutathione is involved in the reduction of selenite to elemental selenium in this organism. Selenium is an essential trace element in the nutrition of many organisms, but it can be highly toxic depending on its concentration and speciation. High selenium concentrations may cause severe abnormalities in the development of various animals and plants (1Ohlendorf H.M. Jacobs L.W. Selenium in Agriculture and the Environment. American Society for Agronomy, Madison, WI1989: 133-177Google Scholar, 2Läuchli A. Bot. Acta. 1993; 106: 455-468Crossref Scopus (195) Google Scholar, 3O'Toole D. Raisbeck M.F. Frankenberger W.T. Engberg R.A. Environmental Chemistry of Selenium. Marcel Dekker, New York1998: 355-395Google Scholar). Deformation and structural modifications have been noted, especially in creatine-formed tissues (i.e. hooves, horns, hair, feather, beaks, and nails) in which appreciable quantities of selenium may accumulate. In these cases, selenium toxicity has been attributed to its ability to replace sulfur in proteins or other sulfur-containing biomolecules. In their investigations of selenite toxicity in prokaryotes, Kramer and Ames (4Kramer G.F. Ames B.N. Mutat. Res. 1988; 201: 169-180Crossref PubMed Scopus (96) Google Scholar) did not observe any nonspecific incorporation of selenium into proteins. They demonstrated that a mutant strain of Salmonella typhimurium, which is able to overexpress oxidative stress proteins such as catalase and superoxide dismutase (SOD), 1The abbreviations used are: SOD, superoxide dismutase; DHPC, diheptanoyl-phosphatidylcholine; EDAX, energy dispersive x-ray analysis; GS-Se-, selenopersulfide of glutathione; GS-Se-SG, selenotrisulfide of glutathione (selenodiglutathione); RS-Se-SR, selenotrisulfides; Se°, elemental selenium.1The abbreviations used are: SOD, superoxide dismutase; DHPC, diheptanoyl-phosphatidylcholine; EDAX, energy dispersive x-ray analysis; GS-Se-, selenopersulfide of glutathione; GS-Se-SG, selenotrisulfide of glutathione (selenodiglutathione); RS-Se-SR, selenotrisulfides; Se°, elemental selenium. is significantly more resistant to selenite toxicity than the wild type. Their results suggest that free radical formation might be involved. They also considered the high reactivity of selenite with sulfhydryl groups and the formation of oxygen radicals when selenium reacted with cysteine or glutathione and concluded that selenite toxicity in bacteria might be the result of oxidative damage. Consistent with these results Bébien et al. (5Bébien M. Lagniel G. Garin J. Touati D. Verméglio A. Labarre J. J. Bacteriol. 2002; 184: 1556-1564Crossref PubMed Scopus (68) Google Scholar) observed that two types of SOD are induced in cultures of Escherichia coli exposed to selenite, thus confirming the involvement of free radicals in selenium toxicity. In addition, glutathione reductase was induced in cultures of Rhodobacter sphaeroides (6Bébien M. Chauvin J.-P. Adriano J.-M. Grosse S. Verméglio A. Appl. Env. Microbiol. 2001; 67: 4440-4447Crossref PubMed Scopus (69) Google Scholar) and E. coli (5Bébien M. Lagniel G. Garin J. Touati D. Verméglio A. Labarre J. J. Bacteriol. 2002; 184: 1556-1564Crossref PubMed Scopus (68) Google Scholar) amended with selenite. In the bacterial domain glutathione is present in the cyanobacteria and the α, β, and γ groups of the proteobacteria (7Newton G.L. Fahey R.C. Viña J. Glutathione: Metabolism and Physiological Functions. CRC Press, Boca Raton, FL1989: 69-77Google Scholar). Considering these data we investigated the chemical reduction of selenite with glutathione and compared the features of this reaction with those of the dissimilatory selenite reduction in R. rubrum and E. coli. In a chemical approach, Painter (8Painter E.P. Chem. Rev. 1941; 28: 179-213Crossref Scopus (245) Google Scholar) observed the high reactivity of selenite with thiol groups. He was the first to demonstrate the formation of selenotrisulfides (RS-Se-SR), according to Reaction 1. 4 RSH+H2SeO3→RS-Se-SR+RSSR+3H2O (REACTION 1) Ganther (9Ganther H.E. Biochemistry. 1971; 10: 4089-4098Crossref PubMed Scopus (302) Google Scholar) studied the reaction of selenite with glutathione (GSH), the most abundant thiol found in the eukaryotic cells, the cyanobacteria, and the α, β, and γ groups of the proteobacteria (7Newton G.L. Fahey R.C. Viña J. Glutathione: Metabolism and Physiological Functions. CRC Press, Boca Raton, FL1989: 69-77Google Scholar). He showed that the selenotrisulfide of glutathione (GS-Se-SG), which was later renamed selenodiglutathione, is a very good substrate for glutathione reductase with Km and Vmax values comparable with those of glutathione itself. He described this with Reaction 2. GS-Se-SG+NADPH→Glutathione reductaseGSH+GS-Se−+NADP+ (REACTION 2) Ganther (9Ganther H.E. Biochemistry. 1971; 10: 4089-4098Crossref PubMed Scopus (302) Google Scholar) also proposed that the unstable selenopersulfide of glutathione (GS-Se-) dismutates into elemental selenium (Se°) and reduced glutathione according to the following stoichiometry. GS-Se−+H+→GSH+Seo (REACTION 3) In experiments about the kinetics of selenite reduction in cultures of Rhodospirillum rubrum we observed that the rate of the reaction is decreased significantly when the organism synthesizes low levels of glutathione. 2J. Kessi, submitted for publication.2J. Kessi, submitted for publication. In the present study, we investigate the kinetics of formation of selenodiglutathione, superoxide anions, and elemental selenium during abiotic (chemical) reduction of selenite by glutathione, and we compare the features of this reaction with those of the reaction mediated by R. rubrum and E. coli. We also compare the properties of the abiotically formed Se° particles with those produced during the bacterial process. Selenite Reduction—Chemical reactions were performed in 50 mm Tris·HCl buffer (pH 7.0) at room temperature in tubes kept anoxic (Hungate, a The buffer was with an for about h of selenite, glutathione, and cytochrome c were also in tubes and with The of and were performed with was a on the formation of a with Chem. PubMed Scopus Google Scholar, J. M. E. M. R. Appl. Microbiol. PubMed Google Scholar). was by its at (9Ganther H.E. Biochemistry. 1971; 10: 4089-4098Crossref PubMed Scopus (302) Google Scholar). and were in a were performed in with superoxide anions are known to cytochrome c J. Chem. PubMed Google superoxide levels can be by the rate of cytochrome c reduction at various during the reaction. The were performed in a of the at were in with and with The reaction was to to the temperature for min cytochrome c was with a with at various reaction The rate of reduction was at The cytochrome c concentration in the and depending on the selenite high concentration of or about SOD was to cytochrome c reduction the described in this oxygen concentration was a The reaction was to the after the of the reaction and for The and were with was the reaction described in et al. G. Acta. Scopus Google Scholar). were performed min after the of the reaction to of the with superoxide anions. was after to selenite with of Se° were in tubes for min at The was and of was to the The tubes were and in the orange-red of Se° was to the tubes for a to the and the were The Se° to selenite was the described for selenite. The presence of Se° in the reaction also be observed of its at not and of Se° The Se° particles were in 50 mm Tris·HCl buffer (pH 7.0) at room temperature a The J. E. R. G. Biochemistry. PubMed Scopus Google Scholar) was to the buffer for a concentration of to and of the particles on the of the The reaction was performed with mm selenite and mm glutathione of The reaction was to for 2 h the Se° particles were for min at at room The was and the particles were with 50 mm Tris·HCl buffer (pH 7.0) 2 mm 2 mm The concentration used is than its concentration of Se° grown cultures of R. rubrum amended with mm selenite were 2 after the phase and were at room temperature for min at the was The Se° particles with J. Bacteriol. PubMed Google was for min at The was in a of 50 mm Tris·HCl buffer (pH 7.0) to of the of the The were by the to a concentration of mm J. E. R. G. Biochemistry. PubMed Scopus Google was at room were by at for min after The was and the the Se° particles was again at for The was in a of 2 mm buffer to about of the of and and of was cells were in for min were with with and in low were in in for in and and in the were with and as described by PubMed Scopus Google Scholar). of Se° particles with a selenium concentration of about mm were a of and observed without any energy dispersive x-ray to of of Se° with a Se° concentration of about mm were on a and the Se° was at room temperature after of were with an The of Selenite by was in the presence of glutathione at room The yield of the reaction was by the to and of the selenite concentrations the reaction in of and and The of selenite decreased when the selenite and concentrations were of selenite, rate of of and of Se° particles in the abiotic reduction of selenite with of was the in for to for the of of the superoxide concentration was the in for Se° to of of the Se° particles was the of the reaction at after of the reaction. The values a of two The was lower than in not The was the in The for the of of the superoxide concentration was the in The of of the Se° particles was the of the reaction at after of the reaction. The values a of two The was lower than in not in a Formation of concentration of selenodiglutathione within the 1st min of the reaction. a maximum within and decreased the The of and of selenodiglutathione were with selenite concentrations and In with a than was in the within a after of the reaction The of paralleled the formation of orange-red Se° with selenite concentration and of by of SOD to the reaction the in selenodiglutathione during the first of the reaction at not that the superoxide anions to the degradation of the Formation of that superoxide concentrations were reached within the 1st min of the reaction for In the the selenite concentration and a of was observed for about min the cytochrome c reduction rate to The superoxide anions about min after the reaction was of the superoxide was in reaction the selenite of this degradation of the superoxide in two a rapid that within the 1st min of the reaction was by a significantly that to min after of the reaction concentrations of and selenite with a degradation of the superoxide Cytochrome c which the presence of was inhibited by the was to the SOD concentration not did not in the reaction a low concentration of was the concentrations were in reaction or mm selenite and a of In the mm selenite low concentrations of and were after and 50 In with mm selenite, concentrations of and were and 50 after the of the reaction. reacted with in concentration in the presence of mm glutathione was investigated for to The reaction reached within a with of the the reaction not also reacted with of Se° of was after min in a reaction mm and mm Formation of Se° of the abiotic formation of Se° are in of the reaction at showed that precipitation of Se° particles a after the of the reaction. precipitation with concentrations of selenite and glutathione to and chemical Se° formation was and after In cases, Se° concentrations decreased after reached a maximum The yield of Se° was low compared with that of the bacterially mediated reaction M. Chauvin J.-P. Adriano J.-M. Grosse S. Verméglio A. Appl. Env. Microbiol. 2001; 67: 4440-4447Crossref PubMed Scopus (69) Google Scholar, Frankenberger W.T. Microbiol. PubMed Scopus Google Scholar, M. G. M. J. Appl. Microbiol. 2001; 67: PubMed Scopus Google Scholar) and was in most by the of to selenite the of as of Se° were low compared with those in reaction with of or They with selenite concentrations and and in selenite concentrations and mm not The selenium particles formed during chemical reduction of selenite by glutathione showed the same characteristic as the particles that are produced in bacterial cultures amended with selenite J. M. E. M. R. Appl. Microbiol. PubMed Google Scholar). The produced in buffer 2 mm mm also the same spherical and as the particles bacterial cultures of the in the reaction the buffer led to the formation of of and biological be that the bacterially produced selenium particles the after the cells by about of the of the particles present in the and not and during of the in cells of R. rubrum observed the the of the particles and which to the size of the particles the of and produced Se° particles the for selenium at and to the and were was observed for the biological particles than for the abiotically produced particles In the chemical reduction of selenite with glutathione more selenite was reduced with a of compared with a of the in Reaction in the the rapid in the of O-2 within the 1st min of the reaction by cytochrome c and the formation of selenodiglutathione that the formation of oxygen radicals during the first of the reaction. The observed of cytochrome c reduction and SOD concentration in the reaction that cytochrome c was reduced by the superoxide These results suggest that Reaction proposed by Painter (8Painter E.P. Chem. Rev. 1941; 28: 179-213Crossref Scopus (245) Google Scholar) and Ganther (9Ganther H.E. Biochemistry. 1971; 10: 4089-4098Crossref PubMed Scopus (302) Google Scholar) be to into the formation of We to the first of the abiotic reduction of selenite with glutathione by Reaction (REACTION to Bébien et al. (5Bébien M. Lagniel G. Garin J. Touati D. Verméglio A. Labarre J. J. Bacteriol. 2002; 184: 1556-1564Crossref PubMed Scopus (68) Google observed a of two types of SOD in E. coli grown in the presence of selenite, we that Reaction 4 also in this organism and that it may the first of the dissimilatory reduction of selenite in cells high levels of glutathione and selenite reduction. In the chemical reaction the superoxide dismutates into oxygen and J. Chem. PubMed Google Scholar) according to Reaction (REACTION The of the formed in this reaction is described In the biological reduction the highly produced during the first of the reaction a of degradation reactions by that are induced during oxidative stress and also These the rapid of oxygen thus oxidative and and In a second is to and reduced glutathione by the glutathione reductase as described by Ganther (9Ganther H.E. Biochemistry. 1971; 10: 4089-4098Crossref PubMed Scopus (302) Google Scholar) and in Reaction 2 in the In a the unstable selenopersulfide into the reduced glutathione and elemental selenium according to Reaction in the is not known this reaction is or of the is in In cultures of many of α, β, or γ proteobacteria amended with to mm selenite the reaction is performed to M. Chauvin J.-P. Adriano J.-M. Grosse S. Verméglio A. Appl. Env. Microbiol. 2001; 67: 4440-4447Crossref PubMed Scopus (69) Google Scholar, J. M. E. M. R. Appl. Microbiol. PubMed Google Scholar, M. G. M. J. Appl. Microbiol. 2001; 67: PubMed Scopus Google Scholar, S. Appl. Microbiol. PubMed Google Scholar). The of selenite concentration that the cells are able to may at in the of oxidative stress for this process. the cells are with in the presence of selenite is the of the into the to reactions of selenite with groups of which observed in tissues by (1Ohlendorf H.M. Jacobs L.W. Selenium in Agriculture and the Environment. American Society for Agronomy, Madison, WI1989: 133-177Google Scholar, 2Läuchli A. Bot. Acta. 1993; 106: 455-468Crossref Scopus (195) Google Scholar, 3O'Toole D. Raisbeck M.F. Frankenberger W.T. Engberg R.A. Environmental Chemistry of Selenium. Marcel Dekker, New York1998: 355-395Google Scholar) may be the result of the of an to the of selenite into the The abiotic degradation of selenodiglutathione may be described by Reaction (REACTION In to the biological reaction in which the reduced glutathione is by the of the glutathione the abiotic reaction to an of glutathione which the reaction The of the abiotic reaction, the of to and Se°, not that of the biological process. the abiotic and the is the of the highly in the reaction which to a of reactions that are in Se° can be by the yield of the abiotic reduction of selenite to elemental selenium on the rate of formation and degradation of and and the rate of formation of also on the rate of Reaction the of Reaction is by the observed of degradation in the presence of SOD, the of the superoxide that the superoxide in the of selenodiglutathione to GS-Se-, according to Reaction (REACTION of the degradation of selenodiglutathione by SOD with the rapid degradation of the superoxide during the first of the reaction, as in that the degradation of superoxide and selenodiglutathione according to Reaction of the superoxide significantly J. Chem. PubMed Google Scholar). The kinetics of this reaction to the of the superoxide degradation in The abiotic degradation of in two 1) The of concentrations in the presence of and D. PubMed Scopus Google Scholar) that can be reduction by according to Reaction (REACTION 2) In with the observed of Se° in the presence of we Reaction (REACTION Considering that selenodiglutathione is a that can be the reaction (9Ganther H.E. Biochemistry. 1971; 10: 4089-4098Crossref PubMed Scopus (302) Google Scholar, M. S. A. PubMed Scopus Google Scholar) and that the glutathione in the reaction we that Reaction more than Reaction the formation of and the of Se° as in the abiotic reduction of selenite with glutathione the of selenite, the rate of superoxide and the of Se° formation at various selenite concentrations support and In to and which the degradation of the superoxide in we have to the of O-2 which may the of the reaction elemental oxygen was in in the abiotic reaction we that the oxygen produced by this reaction was in the radical of reactions and as described by and D. PubMed Scopus Google Scholar). these reactions and are and O-2 is the of reduced glutathione as long as O-2 and are The is in Reaction (REACTION The of Reaction on and the superoxide The reaction is very at in a thiol concentration of about and superoxide in the of the rate for these are in the of D. PubMed Scopus Google Scholar). We that the according to Reaction in the presence of the low concentrations and the O-2 in of and of according to Reaction to lower the rate and the yield of the described by and the of the yield of Se° in the abiotic reduction of selenite with glutathione when the is to Considering 1) the high levels in the of various α, β, and γ proteobacteria (7Newton G.L. Fahey R.C. Viña J. Glutathione: Metabolism and Physiological Functions. CRC Press, Boca Raton, FL1989: 69-77Google Scholar, Acta. PubMed Scopus Google 2Läuchli A. Bot. Acta. 1993; 106: 455-468Crossref Scopus (195) Google Scholar) the high of the glutathione reductase in the degradation of the selenodiglutathione to selenopersulfide and glutathione (9Ganther H.E. Biochemistry. 1971; 10: 4089-4098Crossref PubMed Scopus (302) Google Scholar) 3O'Toole D. Raisbeck M.F. Frankenberger W.T. Engberg R.A. Environmental Chemistry of Selenium. Marcel Dekker, New York1998: 355-395Google Scholar) the high reaction rate observed for selenite reduction by abiotic G.F. Ames B.N. Mutat. Res. 1988; 201: 169-180Crossref PubMed Scopus (96) Google Scholar) the of the selenite reduction rate in R. rubrum with decreased glutathione and the of oxygen radicals in the abiotic reduction of selenite with glutathione and the reaction mediated by E. we suggest that glutathione may be the in the dissimilatory reduction of selenite in this reaction and high levels in their groups may also be involved in the reduction. The reduction of selenite and selenodiglutathione by the reductase of E. coli was described M. S. A. J. Chem. PubMed Google Scholar). of this in the biological dissimilatory reduction of selenite is by the observed of and reductase in cultures of E. coli amended with levels of selenite (5Bébien M. Lagniel G. Garin J. Touati D. Verméglio A. Labarre J. J. Bacteriol. 2002; 184: 1556-1564Crossref PubMed Scopus (68) Google Scholar). In the bacterial domain the cyanobacteria and of the α, β, and γ groups of the proteobacteria are able to glutathione (7Newton G.L. Fahey R.C. Viña J. Glutathione: Metabolism and Physiological Functions. CRC Press, Boca Raton, FL1989: 69-77Google Scholar). Consistent with the involvement of glutathione in the dissimilatory reduction of selenite, various proteobacteria to these groups have been to levels of selenite (6Bébien M. Chauvin J.-P. Adriano J.-M. Grosse S. Verméglio A. Appl. Env. Microbiol. 2001; 67: 4440-4447Crossref PubMed Scopus (69) Google Scholar, J. M. E. M. R. Appl. Microbiol. PubMed Google Scholar, M. G. M. J. Appl. Microbiol. 2001; 67: PubMed Scopus Google Scholar, S. Appl. Microbiol. PubMed Google Scholar). In a of selenite in bacteria demonstrated that most are not able to in the presence of mm selenite S. J. Appl. Bacteriol. PubMed Scopus Google Scholar). the proposed of selenite reduction highly oxygen it in which not oxidative stress of selenite reduction may in which are not able to glutathione (7Newton G.L. Fahey R.C. Viña J. Glutathione: Metabolism and Physiological Functions. CRC Press, Boca Raton, FL1989: 69-77Google Scholar) but can high levels of selenite. for has been to in the presence of to mm selenite S. A. R. Google Scholar). for proteobacteria, a of and reductase has been observed in exposed to concentrations of selenite D. M. E. 10: PubMed Scopus Google Scholar) bacteria and other groups at levels (7Newton G.L. Fahey R.C. Viña J. Glutathione: Metabolism and Physiological Functions. CRC Press, Boca Raton, FL1989: 69-77Google Scholar). a reductase of and other is produced by J. Bacteriol. PubMed Google Scholar). that the of selenite reduction in these bacteria may be to that proposed for the proteobacteria with a high glutathione also be that reduction of can be by which may be present in cells as of the selenium R. J. Chem. Scopus Google Scholar). for a high selenite may be a high of for the reduction of and a oxidative stress The of the Se° particles present in cells of R. rubrum grown in the presence of selenite suggest that the particles the the size of produced Se° The particles which during of the cells, are produced by of the particles that Se° particles the bacterial cultures and the chemical reaction selenium. The observed in the biological particles is by the presence of of present in the biological We are these particles in more The for the formation of superoxide anions during the abiotic reduction of selenite with glutathione in this is with the observed of superoxide in E. coli grown in the presence of selenite (5Bébien M. Lagniel G. Garin J. Touati D. Verméglio A. Labarre J. J. Bacteriol. 2002; 184: 1556-1564Crossref PubMed Scopus (68) Google Scholar). support to the hypothesis that glutathione may be involved in the dissimilatory reduction of selenite in high levels of glutathione. of glutathione in the dissimilatory reduction of selenite in proteobacteria is also with the observed of the selenite reduction rate in R. rubrum low levels of