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The Action of Bismuth against Helicobacter pylori Mimics but Is Not Caused by Intracellular Iron Deprivation. Michael V. Bland, 2004.Helicobacter pylori is highly susceptible to bismuth, a heavy metal with antimicrobial activity linked to its effect on bacterial iron uptake . Three strains of H . pylori were analyzed for indicators of iron limitation following exposure to the MIC of colloidal bismuth subcitrate (MICCBS) . Similar morphologic and outer membrane changes were observed following growth in iron-limiting medium and at the MICCBS that inhibited the growth of all three strains . These changes, which were also observed for iron-limited bacteria, were alleviated by the addition of iron to the cultures . H . pylori ATP levels, reduced in iron-limiting medium, were below the limits of detection in two of the three strains following exposure to bismuth . The addition of iron partially restored bacterial ATP levels in these two strains, although not to normal concentrations . In contrast, exposure of the same strains to the MICCBS failed to deplete intracellular levels of iron, which were significantly reduced by culturing in iron-limiting medium . Thus, the antimicrobial effect of bismuth and of iron limitation on H . pylori may be similar . However, the respective mechanisms of intracellular action would appear to be mediated by different pathways within the cell . Blakeslea trispora Genes for Carotene Biosynthesis. M. Rodríguez-Sáiz, 2004. Involvement of Superoxide Dismutases in the Response of Escherichia coli to Selenium Oxides. Magali Bébien, 2002.Selenium can provoke contrasting effects on living organisms . It is an essential trace element, and low concentrations have beneficial effects, such as the reduction of the incidence of cancer . However, higher concentrations of selenium salts can be toxic and mutagenic . The bases for both toxicity and protection are not clearly understood . To provide insights into these mechanisms, we analyzed the proteomic response of Escherichia coli cells to selenate and selenite treatment under aerobic conditions . We identified 23 proteins induced by both oxides and ca . 20 proteins specifically induced by each oxide . A striking result was the selenite induction of 8 enzymes with antioxidant properties, particularly the manganese and iron superoxide dismutases (SodA and SodB) . The selenium inductions of sodA and sodB were controlled by the transcriptional regulators SoxRS and Fur, respectively . Strains with decreased superoxide dismutase activities were severely impaired in selenium oxide tolerance . Pretreatment with a sublethal selenite concentration triggered an adaptive response dependent upon SoxRS, conferring increased selenite tolerance . Altogether, our data indicate that superoxide dismutase activity is essential for the cellular defense against selenium salts, suggesting that superoxide production is a major mechanism of selenium toxicity under aerobic conditions . Construction and Screening of Metagenomic Libraries Derived from Enrichment Cultures: Generation of a Gene Bank for Genes Conferring Alcohol Oxidoreductase Activity on Escherichia coli. Anja Knietsch, 2003.Enrichment of microorganisms with special traits and the construction of metagenomic libraries by direct cloning of environmental DNA have great potential for identifying genes and gene products for biotechnological purposes . We have combined these techniques to isolate novel genes conferring oxidation of short-chain (C2 to C4) polyols or reduction of the corresponding carbonyls . In order to favor the growth of microorganisms containing the targeted genes, samples collected from four different environments were incubated in the presence of glycerol and 1,2-propanediol . Subsequently, the DNA was extracted from the four samples and used to construct complex plasmid libraries . Approximately 100,000 Escherichia coli strains of each library per test substrate were screened for the production of carbonyls from polyols on indicator agar . Twenty-four positive E . coli clones were obtained during the initial screen . Sixteen of them contained a plasmid (pAK101 to pAK116) which conferred a stable carbonyl-forming phenotype . Eight of the positive clones exhibited NAD(H)-dependent alcohol oxidoreductase activity with polyols or carbonyls as the substrates in crude extracts . Sequencing revealed that the inserts of pAK101 to pAK116 encoded 36 complete and 17 incomplete presumptive protein-encoding genes . Fifty of these genes showed similarity to sequenced genes from a broad collection of different microorganisms . The genes responsible for the carbonyl formation of E . coli were identified for nine of the plasmids (pAK101, pAK102, pAK105, pAK107 to pAK110, pAK115, and pAK116) . Analyses of the amino acid sequences deduced from these genes revealed that three (orf12, orf14, and orf22) encoded novel alcohol dehydrogenases of different types, four (orf5, sucB, fdhD, and yabF) encoded novel putative oxidoreductases belonging to groups distinct from alcohol dehydrogenases, one (glpK) encoded a putative glycerol kinase, and one (orf1) encoded a protein which showed no similarity to any other known gene product .
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