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1.
Oxidative metabolism of inorganic sulfur compounds by bacteria   总被引:19,自引:0,他引:19  
The history of the elucidation of the microbiology and biochemistry of the oxidation of inorganic sulfur compounds in chemolithotrophic bacteria is briefly reviewed, and the contribution of Martinus Beijerinck to the study of sulfur-oxidizing bacteria highlighted. Recent developments in the biochemistry, enzymology and molecular biology of sulfur oxidation in obligately and facultatively lithotrophic bacteria are summarized, and the existence of at least two major pathways of thiosulfate (sulfur and sulfide) oxidation confirmed. These are identified as the Paracoccus sulfur oxidation (or PSO) pathway and the S4intermediate (or S4I) pathway respectively. The former occurs in organisms such as Paracoccus (Thiobacillus) versutus and P. denitrificans, and possibly in Thiobacillus novellus and Xanthobacter spp. The latter pathway is characteristic of the obligate chemolithotrophs (e.g. Thiobacillus tepidarius, T. neapolitanus, T. ferrooxidans, T. thiooxidans) and facultative species such as T. acidophilus and T. aquaesulis, all of which can produce or oxidize tetrathionate when grown on thiosulfate. The central problem, as yet incompletely resolved in all cases, is the enzymology of the conversion of sulfane-sulfur (as in the outer [S-] atom of thiosulfate [-S-SO3-]), or sulfur itself, to sulfate, and whether sulfite is involved as a free intermediate in this process in all, or only some, cases. The study of inorganic sulfur compound oxidation for energetic purposes in bacteria (i.e. chemolithotrophy and sulfur photolithotrophy) poses challenges for comparative biochemistry. It also provides evidence of convergent evolution among diverse bacterial groups to achieve the end of energy-yielding sulfur compound oxidation (to drive autotrophic growth on carbon dioxide) but using a variety of enzymological systems, which share some common features. Some new data are presented on the oxidation of 35S-thiosulfate, and on the effect of other anions (selenate, molybdate, tu ngstate, chromate, vanadate) on sulfur compound oxidation, including observations which relate to the roles of polythionates and elemental sulfur as intermediates.  相似文献
2.
Depleted mucosal antioxidant defences in inflammatory bowel disease   总被引:16,自引:0,他引:16  
Experimental approaches designed to define the role of reactive oxygen and nitrogen species generated by inflammatory cells in the tissue injury seen in inflammatory bowel disease rarely consider the chemical antioxidant defences against such increased oxidant stress in the mucosa. In this investigation, we have analysed components of the aqueous and lipid phase antioxidant mucosal defences by measuring the total peroxyl radical scavenging capacity and the levels of urate, glutathione, -tocopherol, and ubiquinol-10 in paired noninflamed and inflamed mucosal biopsies from inflammatory bowel disease patients. Compared to paired noninflamed mucosa, decreases were observed in inflamed mucosa for total peroxyl radical scavenging capacity (55%, p = 0.0031), urate [Crohn's disease (CD), 62.2%, p = 0.066; ulcerative colitis (UC), 47.3%, p = 0.031], glutathione (UC, 59%, 7/8 patients, ns), total glutathione (UC 65.2%, 6/8 patients, ns), ubiquinol-10 (CD, 75.7%, p = 0.03; UC, 90.5%, p = 0.005). The mean -tocopherol content was unchanged. These observations support our earlier findings of decreased reduced and total ascorbic acid in inflamed IBD mucosa and demonstrate that the loss of chemical antioxidant defences affects almost all the major components. The decreased antioxidant defences may severely compromise the inflamed mucosa, rendering it more susceptible to oxidative tissue damage, hindering recovery of the mucosa and return of epithelial cell layer integrity. The loss of chemical antioxidant components provides a strong rationale for developing novel antioxidant therapies for the treatment of inflammatory bowel disease.  相似文献
3.
A new therapeutic approach for inflammatory bowel diseases is based on the administration of probiotic bacteria. Prokaryotic DNA contains unmethylated CpG motifs which can activate immune responses, but it is unknown whether bacterial DNA is involved in the beneficial effects obtained by probiotic treatment. Peripheral blood mononuclear cells (PBMC) from healthy donors were incubated with pure DNA of eight probiotic strains and with total bacterial DNA from human feces collected before and after probiotic ingestion. Cytokine production was analyzed in culture supernatants. Modification of human microflora after probiotic administration was proven by polymerase chain reaction analysis. Here we show that Bifidobacterium genomic DNA induced secretion of the antiinflammatory interleukin-10 by PBMC. Total bacterial DNA from feces collected after probiotic administration modulated the immune response by a decrease of interleukin-1 beta and an increase of interleukin-10.  相似文献
4.
Desulfovibrio vulgaris (Marburg) was grown on H2 plus sulfate and H2 plus thiosulfate as the sole energy sources and acetate plus CO2 as the sole carbon sources. Conditions are described under which the bacteria grew exponentially. Specific growth rates () and molar growth yields (Y) at different pH were determined. and Y were found to be strongly dependent on the pH. Highest growth rates and molar growth yields were observed for growth on H2 plus sulfate at pH 6.5 (=0.15h-1; Y SO 4 2- =8.3g·mol-1) and for growth on H2 plus thiosulfate at pH 6.8 (=0.21h-1; Y S 2O 3 2 =16.9g·mol-1).The growth yields were found to increase with increasing growth rates: plots of 1/Y versus 1/ were linear. Via extrapolation to infinite growth rates a Y SO4 2- /max of 12.2g·mol-1 and a YS2O 3 2- /max of 33.5g·mol-1 was obtained.The growth yield data are interpred to indicate that dissimilatory sulfate reduction to sulfide is associated with a net synthesis of 1 mol of ATP and that near to 3 mol of ATP are formed during dissimilatory sulfite reduction to sulfide.  相似文献
5.
Abstract The survival after oxygen stress was studied with eight species of sulfate-reducing bacteria. In the absence of sulfide all species tolerated 6 min of aeration without loss of viability. Even after 3 h of aeration the viability of four species ( Desulfovibrio vulgaris, D. desulfuricans, D. salexigens and Desulfobacter postgatei ) was not impaired. Four other species were sensitive to 3 h of aeration: the surviving fractions of Desulfotomaculum ruminis, D. nigrificans and Desulfococcus multivorans were about 1%, that of Desulfotomaculum orientis about 0.01%. Formation of spores resulted in oxygen resistance of D. orientis . Reducing agents did not protect the vegetative cells of this strain against oxygen toxicity. In contrast, sulfhydryl group-containing agents increased the oxygen sensitivity considerably.
Growth of sulfate- and sulfur-reducing bacteria in oxygen-sulfide gradients in agar tubes was studied. In the gradients these strictly anaerobic bacteria revealed oxygen-dependent growth in sulfate- and sulfur-free medium. Three sulfate-reducing bacteria that could not use thiosulfate or sulfur as electron acceptor failed to grow in oxygen-sulfide gradients. Obviously, not directly molecular oxygen, but oxidation products of sulfide, such as thiosulfate or sulfur, were used as electron acceptors and were continuously regenerated in a cycling process from sulfide by autoxidation. The conceivable ecological significance of a short sulfur cycle driven by autoxidation of sulfide is discussed.  相似文献
6.
Ethylene as promoter of wheat grain maturation and ear senescence   总被引:12,自引:0,他引:12  
This work was aimed at testing the involvement of ethylene in the maturation of grain and senescence of the foliar structures of the wheat inflorescence. Whole wheat ears emitted ethylene to the atmosphere. From pre-anthesis, ethylene emission progressively increased from 0.76 nl g–1FW h–1 to a peak 1.53 nl g–1FW h–1 at the hard dough stage of the grains, to fall to a minimum of 0.10 nl g–1FW h–1 at the dormant seed stage. Ethephon increased the ethylene release, hastened the process of grain maturation and senescence of the ears. Aminoethoxyvinylglycine and silver thiosulfate produced the opposite effects. It is concluded that ethylene plays a role in grain maturation and in the senescence of the green bracts of the inflorescence.Abbreviations Ag+ = silver ion - AVG = aminoethoxyvinylglycine - SAM = S-adenosylmethionine - STS = silver thiosulfate - TGW = thousand grain weight Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET)  相似文献
7.
Growth rate stimulation of marine pseudomonads by thiosulfate   总被引:10,自引:0,他引:10  
The oxidation of thiosulfate to tetrathionate exerts a definite growth rate stimulation in glucose, acetate, and yeast extract cultures of some marine pseudomonads. The failure to find this effect in earlier studies with terrestrial isolates may lie in the particular conditions used in the present experiments (constant pH, high ratio of thiosulfate to organic substrate) or in the different metabolic characteristics of the marine isolates.Contribution No. 3220 from the Woods Hole Oceanographic Institution.  相似文献
8.
Abstract: Different reduced sulfur compounds (H2S, FeS, S2O32−) were tested as electron donors for dissimilatory nitrate reduction in nitrate-amended sediment slurries. Only in the free sulfide-enriched slurries was nitrate appreciably reduced to ammonia (     ), with concomitant oxidation of sulfide to S0 (     ). The initial concentration of free sulfide appears as a factor determining the type of nitrate reduction. At extremely low concentrations of free S2− (metal sulfides) nitrate was reduced via denitrification whereas at higher S2− concentrations, dissimilatory nitrate reduction to ammonia (DNRA) and incomplete denitrification to gaseous nitrogen oxides took place. Sulfide inhibition of NO- and N2O- reductases is proposed as being responsible for the driving part of the electron flow from S2− to NH4+.  相似文献
9.
Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 108 cells of sulfate reducers cm−3 sediment, 2.0 × 109 cells of chemolithoautotrophs cm−3 sediment, and 4.0 × 107 cells of anoxygenic phototrophs cm−3 sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm−3 d−1 in the absence of oxygen, and 123 nmol cm−3 d−1 in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm−3 d−1). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate.  相似文献
10.
Increase in reactive oxygen species plays an integral part in the inflammatory response, and chronic inflammation increases cancer risk. Selenium-dependent glutathione peroxidase (GPX) is well recognized for its antioxidant, and thus anti-inflammatory, activity. However, due to the multiple antioxidant families present in the gastrointestinal tract, it has been difficult to demonstrate the importance of individual antioxidant enzymes. Using genetically altered mice deficient in individual Gpx genes has provided insight into the physiological functions of these genes. Insufficient GPX activity in the mucosal epithelium can trigger acute and chronic inflammation. The presence of certain microflora, such as Helicobacter species, may affect cancer risk significantly. However, when damaged cells have progressed into a precancerous status, increased GPX activity may become procarcinogenic, presumably due to inhibition of hydroperoxide-mediated apoptosis. This review summarizes the current view of GPX in inflammation and cancer with emphasis on the GI tract.  相似文献
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