Heavy metal resistance patterns of Frankia strains

The sensitivity of 12 Frankia strains to heavy metals was determined by a growth inhibition assay. In general, all of the strains were sensitive to low concentrations (<0.5 mM) of Ag(1+), AsO(2)(1-), Cd(2+), SbO(2)(1-), and Ni(2+), but most of the strains were less sensitive to Pb(2+) (6 to 8 mM), CrO(4)(2-) (1.0 to 1.75 mM), AsO(4)(3-) (>50 mM), and SeO(2)(2-) (1.5 to 3.5 mM). While most strains were sensitive to 0.1 mM Cu(2+), four strains were resistant to elevated levels of Cu(2+) (2 to 5 mM and concentrations as high as 20 mM). The mechanism of SeO(2)(2-) resistance seems to involve reduction of the selenite oxyanion to insoluble elemental selenium, whereas Pb(2+) resistance and Cu(2+) resistance may involve sequestration or binding mechanisms. Indications of the resistance mechanisms for the other heavy metals were not as clear.     

Reduction of Selenium Oxyanions by Enterobacter cloacae SLD1a-1: Isolation and Growth of the Bacterium and Its Expulsion of Selenium Particles

A facultative bacterium capable of removing the selenium (Se) oxyanions selenate (SeO(inf4)(sup2-)) and selenite (SeO(inf3)(sup2-)) from solution culture in flasks open to the atmosphere was isolated and studied with the goal of assessing its potential for use in bioremediation of seleniferous agricultural drainage water. Elemental Se (Se(sup0)) was confirmed as a product of the reaction. The organism, identified as Enterobacter cloacae and designated strain SLD1a-1 (ATCC 700258), removed from 61.5 to 94.5% of added SeO(inf4)(sup2-) (the primary species present in agricultural drainage water) at concentrations from 13 to 1,266 (mu)M. Equimolar amounts of nitrate (NO(inf3)(sup-)), which interferes with SeO(inf4)(sup2-) reduction in some organisms, did not influence the reaction in growth experiments but had a slight inhibitory effect in a washed-cell suspension. Washed-cell suspension experiments also showed that (i) SeO(inf3)(sup2-) is a transitory intermediate in reduction of SeO(inf4)(sup2-), being produced and rapidly reduced concomitantly; (ii) NO(inf3)(sup-) is also reduced concomitantly and at a much higher rate than SeO(inf4)(sup2-); and (iii) although enzymatic, reduction of either oxyanion does not appear to be an inducible process. Transmission electron microscopy revealed that precipitate particles are <0.1 (mu)m in diameter, and these particles were observed free in the medium. Evidence indicates that SLD1a-1 uses SeO(inf4)(sup2-) as an alternate electron acceptor and that the reaction occurs via a membrane-associated reductase(s) followed by rapid expulsion of the Se particles.     

Selenite-reducing capacity of the copper-containing nitrite reductase of Rhizobium sullae

Rhizobium sullae strain HCNT1 contains a nitric oxide-producing nitrite reductase of unknown function due to the absence of a complementary nitric oxide reductase. HCNT1 had the ability to grow on selenite concentrations as high as 50 mM, and during growth, selenite was reduced to the less toxic elemental selenium. An HCNT1 mutant lacking nitrite reductase grew poorly in the presence of 5 mM selenite, was unable to grow in the presence of 25 or 50 mM selenite and also showed no evidence of selenite reduction. A naturally occurring nitrite reductase-deficient R. sullae strain, CC1335, also showed little growth on the higher concentrations of selenite. Mobilization of a plasmid containing the HCNT1 gene encoding nitrite reductase into CC1335 increased its resistance to selenite. To confirm that this ability to grow in the presence of high concentrations of selenite correlated with nitrite reductase activity, a new nitrite reductase-containing strain was isolated from the same location where HCNT1 was isolated. This strain was also resistant to high concentrations of selenite. Inactivation of the gene encoding nitrite reductase in this strain increased selenite sensitivity. These data suggest that the nitrite reductase of R. sullae provides resistance to selenite and offers an explanation for the radically truncated denitrification found uniquely in this bacterium.     

Selenium metabolism in Escherichia coli

Escherichia coli will reduce selenite (SeO 3 2- ) andselenate (SeO 4 2- ) to elemental selenium Se 0 . Seleniumwill also become incorporated intoproteins as part of the amino acids selenocysteine or selenomethionine.The reaction of selenitewith glutathione produces selenodiglutathione (GS-Se-GS). Selenodiglutathioneand itssubsequent reduction to glutathioselenol (GS-SeH) are likely the key intermediatesin the possiblemetabolic fates of selenium. This review presents the possible pathwaysinvolving selenium in E. coli. Identification of intermediates and potentialprocesses from uptake of the toxic oxyanions through to theirdetoxification will assist us inunderstanding the complexities of metalloid oxyanion metabolism in thesebacteria.     

Hydrogenase I of Clostridium pasteurianum functions as a novel selenite reductase

Clostridium pasteurianum's hydrogenase I, an important constitutive metabolic enzyme, has been shown to function as a 'novel selenite reductase'. Selenite reductase activity was found to co-purify with hydrogenase I activity; the fold purification and specific activities for these two activities paralleled each other throughout the purification steps. The highly purified hydrogenase I apparent K(m) for the selenite substrate was 0.2 mM. The stoichiometry for the enzymatic reduction of SeO3(2-) to Se(0) via H2 oxidation, was determined to be 2.3:1 (H2:Se(0)), very close to the theoretical ratio of 2:1 for this reduction reaction. Known electron carriers required for hydrogenase I activity were also found to couple its selenite reductase activity, the most efficient one being ferredoxin. The purified hydrogenase I not only reduced selenite but also tellurite, and its selenite activity was completely inhibited by O2 and CuSO4, potent inhibitors of hydrogenase I activity.     

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

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 (Se⁰). Hence, SES-3 can carry out a complete reduction of selenate to Se⁰. 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 [¹⁴C]lactate to ¹⁴CO₂ 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 Se⁰ 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 Se⁰. 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 Se⁰ may proceed, in part, by some of the components of a dissimilatory system for sulfur oxyanions.     

Rhizosphere-induced selenium precipitation for possible applications in phytoremediation of se polluted effluents

Two bacterial isolates were obtained in axenic culture from the rhizosphere soil of Astragalus bisulcatus, a legume able to hyperaccumulate selenium. Both strains resulted of particular interest for their high resistance to the toxic oxyanion SeO3(2-) (selenite, Se(IV)). On the basis of molecular and biochemical analyses, these two isolates were attributed to the species Bacillus mycoides and Stenotrophomonas maltophilia, respectively. Their capability in axenic culture to precipitate the soluble, bioavailable and highly toxic selenium form selenite to insoluble and relatively non-toxic Se(0) (elemental selenium) was evaluated in defined medium added with 0.2 or 0.5 mM Se(IV). Both strains showed to completely reduce 0.2 mM selenite in 120 h, while 0.5 mM Se(IV) was reduced up to 67% of the initial concentration by B. mycoides and to about 50% by S. maltophilia in 48 h. Together in a dual consortium, B. mycoides and S. maltophilia increased the kinetics of selenite reduction, thus improving the efficiency of the process. A model system for selenium rhizofiltration based on plant-rhizobacteria interactions has been proposed.     

Fate of selenate and selenite metabolized by Rhodobacter sphaeroides

Cultures of a purple nonsulfur bacterium, Rhodobacter sphaeroides, amended with approximately 1 or approximately 100 ppm selenate or selenite, were grown phototrophically to stationary phase. Analyses of culture headspace, separated cells, and filtered culture supernatant were carried out using gas chromatography, X-ray absorption spectroscopy, and inductively coupled plasma spectroscopy-mass spectrometry, respectively. While selenium-amended cultures showed much higher amounts of SeO(3)(2-) bioconversion than did analogous selenate experiments (94% uptake for SeO(3)(2-) as compared to 9.6% for SeO(4)(2-)-amended cultures from 100-ppm solutions), the chemical forms of selenium in the microbial cells were not very different except at exposure to high concentrations of selenite. Volatilization accounted for only a very small portion of the accumulated selenium; most was present in organic forms and the red elemental form.     

还原亚硒酸盐产生红色单质硒光合细菌菌株的筛选与鉴定

从实验室保藏的光合细菌中筛选出一株对亚硒酸钠还原效率较高的菌株S3,其亚硒酸钠还原产物通过透射电子显微镜及EDX(Electron-Dispersive X-ray)分析确定为红色单质硒。菌株S3的形态学特征、生理生化特征及光合色素扫描结果与固氮红细菌(Rhodobacter azotoformans)的特征基本一致;16S rDNA序列(GenBank登录号为DQ402051)在系统发育树中与固氮红细菌同属一个类群,序列同源性为99%。根据上述结果将菌株S3鉴定为固氮红细菌。初步研究了该菌株还原亚硒酸钠的特性,首次报道固氮红细菌具有还原亚硒酸盐产生红色单质硒的能力,为今后利用微生物方法治理环境中硒污染、利用微生物方法获得活性红色单质硒以及对微生物还原亚硒酸盐产生红色单质硒的机理研究奠定了良好的基础。     

Sister-chromatid exchange induction by sodium selenite: reduced glutathione converts Na2SeO3 to its SCE-inducing form

Sodium selenite (Na2SeO3) is an anticarcinogenic/antimutagenic agent that exhibits carcinogenic/mutagenic properties in some short-term test systems used for the detection of DNA-damaging agents. One such test system is sister-chromatid exchange (SCE) induction. Na2SeO3 induces SCEs only if red blood cells (RBCs) are present to 'activate' it to its SCE-inducing form. Here, the ability of reduced glutathione, a major component of RBCs, to serve as an RBC substitute in the activation of Na2SeO3 was determined. Reduced glutathione (10(-4) and 10(-3) M) was shown to be as capable as RBCs in activating Na2SeO3 (7.95 X 10(-6) M) to its SCE-inducing form. These data suggest strongly that the pathway normally utilized by RBCs in the metabolism of Na2SeO3 is the same as that in which Na2SeO3 is converted to its SCE-inducing form.     

An <Emphasis Type="Italic">Azospira oryzae</Emphasis> (syn <Emphasis Type="Italic">Dechlorosoma suillum</Emphasis>) Strain That Reduces Selenate and Selenite to Elemental Red Selenium

A bacterium that reduces the soluble selenium oxyanions, selenate and selenite, to insoluble elemental red selenium (Se⁰) was isolated from a laboratory reactor developed to remove selenate from groundwater. Gene sequence alignment of the 16S rRNA allowed identification of the isolate as Azospira oryzae. Biochemical and morphologic characterization confirm the identification. The isolate reduces selenate and selenite to Se⁰ under microaerophilic and denitrifying conditions but not under aerobic conditions. It does not use selenate or selenite as terminal eˉ donors. Se oxyanion reduction causes the formation of Se nanospheres that are 0.25 ± 0.04 μm in diameter. Nanospheres may be associated with the cells or free in the medium. The enzymatic activity associated with the reduction of selenate has a molecular mass of approximately 500 kD, and the enzymatic activity associated with the reduction of selenite has a mass of approximately 55 kD. Selenite reduction was inhibited by tungsten. The molecular masses of these activities were different from those associated with the reduction of dimethylsulfoxide, sulfate, and nitrite. This bacterium, or perhaps its enzymes or DNA, might be useful for the remediation of waters contaminated with Se oxyanions.     

Selenite stress elicits physiological adaptations in Bacillus sp. (strain JS-2)

A bacterial isolate (strain JS-2) characterized as Bacillus sp. was challenged with high concentrations of toxic selenite ions. The microbe was found to transform the toxic, soluble, colorless selenite (SeO(3)(2-)) oxyions to nontoxic, insoluble, red elemental selenium (Se(0)). This process of biotransformation was accompanied by cytoplasmic and surface accumulation of electron dense selenium (Se(0)) granules, as revealed in electron micrographs. The cells grown in the presence of selenite oxyions secreted large quantities of extracellular polymeric substances (EPS). There were quantitative and qualitative differences in the cell wall fatty acids of the culture grown in the presence of selenite ions. The relative percentage of total saturated fatty acid and cyclic fatty acid increased significantly, whereas the amount of total unsaturated fatty acids decreased when the cells were exposed to selenite stress. All these physiological adaptive responses evidently indicate a potentially important role of cell wall fatty acids and extracellular polymeric substances in determining bacterial adaptation towards selenite-induced toxicity, which thereby explains the remarkable competitiveness and ability of this microbe to survive the environmental stress.     

Synthesis, characterization, and cytotoxic studies of alpha-diimine/1,2-diamine platinum(II) and palladium(II) complexes of selenite and tellurite and binding of some of these complexes to DNA.

Eleven new complexes of formula [M(NN)(XO3)] (where M is Pd(II) or Pt(II); NN is 2,2'-bipyridine, 1,10-phenanthroline, 2,2'-dipyridylamine, ethylenediamine or (+-)trans-1,2-diaminocyclohexane, and XO3(2-) is SeO3(2-) or TeO3(2-)) have been synthesized. These water soluble complexes have been characterized by chemical analysis and conductivity measurements as well as ultraviolet-visible and infrared spectroscopy. In these complexes the selenite or tellurite ligand coordinates to platinum(II) or palladium(II) as bidentate with two oxygen atoms. These complexes inhibit the growth of P 388 lymphocytic leukemia cells, their targets are DNA. The selenite complexes invariably show I.D.50 values less than cisplatin. However, the I.D.50 values of the tellurite complexes are usually higher than cisplatin, except that of [Pd(dach)(TeO3)] which has comparable I.D.50 values, as compared to cisplatin. [Pt(bipy)(SeO3)] and [Pd(bipy)(SeO3)] have been interacted with calf thymus DNA and bind to DNA through a coordinate covalent bond.     

箬叶多糖及其化学修饰物、亚硒酸钠和GSH对Cu~(2+)诱导的LDL氧化修饰的保护作用

研究了箬叶多糖ＦⅢ－ａ及其化学修饰物、亚硒酸钠和ＧＳＨ对Ｃｕ２＋诱导的低密度脂蛋白氧化修饰的保护作用．其结果表明箬叶多糖、硫酸酯多糖、硒酸酯多糖可显著抑制脂质过氧化产物（ＴＢＡＲＳ）及荧光物质的生成,彼此之间无明显差异．但对ＶＥ的消耗有着不同的保护作用,其顺序是ＦⅢ－ａ＞Ｓ－ＦⅢ－ａ＞Ｓｅ－ＦⅢ－ａ,并且具有明显的量效关系．硒或ＧＳＨ对Ｃｕ２＋诱导的ＬＤＬ氧化修饰无明显的抑制,但联合使用在０．１２５ｍｍｏｌ／ＬＮａ２ＳｅＯ３和０．２ｍｍｏｌ／ＬＧＳＨ及１２．５μｍｏｌ／ＬＮａ２ＳｅＯ３和０．０２ｍｍｏｌ／ＬＧＳＨ的浓度下能强烈地抑制ＴＢＡＲＳ的生成,甚至比正常的ＬＤＬ还要低．但是对ＶＥ的消耗只有较弱的保护作用,硒酸酯多糖与此相似．Ｎａ２ＳｅＯ３在０．１２５ｍｍｏｌ／Ｌ时可以明显抑制荧光物质的生成．     

Effect of selenite on growth and protein synthesis in the phototrophic bacterium Rhodobacter sphaeroides

The effect of selenite on the growth rate and protein synthesis has been investigated in Rhodobacter sphaeroides. This photosynthetic bacterium efficiently reduces selenite with intracellular accumulation under both dark aerobic and anaerobic photosynthetic conditions. Addition of 1 mM selenite under these two growth conditions does not affect the final cell density, although a marked slowdown in growth rate is observed under aerobic growth. The proteome analysis of selenite response by two-dimensional gel electrophoresis shows an enhanced synthesis of some chaperones, an elongation factor, and enzymes associated to oxidative stress. The induction of these antioxidant proteins confirms that the major toxic effect of selenite is the formation of reactive oxygen species during its metabolism. In addition, we show that one mutant unable to precipitate selenite, selected from a transposon library, is affected in the smoK gene. This encodes a constituent of a putative ABC transporter implicated in the uptake of polyols. This mutant is less sensitive to selenite and does not express stress proteins identified in the wild type in response to selenite. This suggests that the entry of selenite into the cytoplasm is mediated by a polyol transporter in R. sphaeroides.     

Mutagenic activity of selenium compounds.

The mutagenicities of selenate (SeO2/4-) and selenite (SeO2/3-) were determined by two bacterial assay systems: Kada's rec-assay and Ames's Salmonella test. In both assays, these compounds were found to be weak mutagens. In the Salmonella test, selenate (0.05 revertants/nmole) and selenite (0.2 revertants/nmole) gave rise to base-pair substitution.     

Effect of Selenite on Growth and Protein Synthesis in the Phototrophic Bacterium Rhodobacter sphaeroides

The effect of selenite on the growth rate and protein synthesis has been investigated in Rhodobacter sphaeroides. This photosynthetic bacterium efficiently reduces selenite with intracellular accumulation under both dark aerobic and anaerobic photosynthetic conditions. Addition of 1 mM selenite under these two growth conditions does not affect the final cell density, although a marked slowdown in growth rate is observed under aerobic growth. The proteome analysis of selenite response by two-dimensional gel electrophoresis shows an enhanced synthesis of some chaperones, an elongation factor, and enzymes associated to oxidative stress. The induction of these antioxidant proteins confirms that the major toxic effect of selenite is the formation of reactive oxygen species during its metabolism. In addition, we show that one mutant unable to precipitate selenite, selected from a transposon library, is affected in the smoK gene. This encodes a constituent of a putative ABC transporter implicated in the uptake of polyols. This mutant is less sensitive to selenite and does not express stress proteins identified in the wild type in response to selenite. This suggests that the entry of selenite into the cytoplasm is mediated by a polyol transporter in R. sphaeroides.     

细菌还原氧化态硒产生红色单质硒的研究进展

硒是一种生命必需的微量元素,但高浓度时毒性较强且会造成环境污染。许多细菌可以将亚硒酸盐(SeO32-)或硒酸盐(SeO42-)等毒性较高的氧化态硒还原为毒性较小的红色单质硒(Se°),形成硒-蛋白复合物,它们对于获得最佳补硒方式和治理硒环境污染具有应用潜力。近年来,关于这一生物还原过程,人们进行了大量的研究,包括碳源、氧气、元素硫、谷胱甘肽以及一些氧化还原酶和膜转运蛋白等在内的多种物质都被发现可能影响或参与了细菌对硒的代谢。综述了细菌进行生物还原氧化态硒的影响因素及不同细菌产生红色单质硒机理的研究进展。