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Extracellular Iron Reduction Is Mediated in Part by Neutral Red and Hydrogenase in Escherichia coli. James B. McKinlay, 2004.Both microbial iron reduction and microbial reduction of anodes in fuel cells can occur by way of soluble electron mediators . To test whether neutral red (NR) mediates iron reduction, as it does anode reduction, by Escherichia coli, ferrous iron levels were monitored in anaerobic cultures grown with amorphous iron oxide . Ferrous iron levels were 19.4 times higher in cultures fermenting pyruvate in the presence of NR than in the absence of NR . NR did not stimulate iron reduction in cultures respiring with nitrate . To explore the mechanism of NR-mediated iron reduction, cell extracts of E . coli were used . Cell extract-NADH-NR mixtures had an enzymatic iron reduction rate almost 15-fold higher than the chemical NR-mediated iron reduction rate observed in controls with no cell extract . Hydrogen was consumed during stationary phase (in which iron reduction was detectable) especially in cultures containing both NR and iron oxide . An E . coli hypE mutant, with no hydrogenase activity, was also impaired in NR-mediated iron reduction activity . NR-mediated iron reduction rates by cell extracts were 1.5 to 2 times higher with hydrogen or formate as the electron source than with NADH . Our findings suggest that hydrogenase donates electrons to NR for extracellular iron reduction . This process appears to be analogous to those of iron reduction by bacteria that use soluble electron mediators (e.g., humic acids and 2,6-anthraquinone disulfonate) and of anode reduction by bacteria using soluble mediators (e.g., NR and thionin) in microbial fuel cells . Characterization of the HspR-Mediated Stress Response in Helicobacter pylori. Gunther Spohn, 2002.The major heat shock genes of Helicobacter pylori are regulated by the HspR repressor . In the present study we characterize the transcriptional response of the three known HspR-dependent promoters Pcbp, Pgro, and Phrc to different environmental stresses . A temperature shift from 37 to 42°C causes a typical heat shock response at all three promoters characterized by an immediate and strong induction phase of transcription and a subsequent adaptation phase, which is specific for each promoter and whose onset is determined partially by the half-lives of the respective mRNAs . Exposure to high osmolarity induces a similar response on the Pgro and Pcbp promoters while no such response is detectable at the Phrc promoter . Puromycin treatment induces transcription from all three HspR-dependent promoters, indicating that different environmental stresses are intracellularly sensed by the regulatory machinery through the accumulation of nonnative proteins . The implications of these data for the regulatory network controlling the heat shock response in H . pylori are discussed . Identification in Methicillin-Susceptible Staphylococcus hominis of an Active Primordial Mobile Genetic Element for the Staphylococcal Cassette Chromosome mec of Methicillin-Resistant Staphylococcus aureus. Yuki Katayama, 2003.We previously reported that the methicillin resistance gene mecA is carried by a novel type of mobile genetic element, SCCmec (staphylococcal cassette chromosome mec), in the chromosome of methicillin-resistant Staphylococcus aureus (MRSA) . These elements are precisely excised from the chromosome and integrated into a specific site on the recipient chromosome by a pair of recombinase proteins encoded by the cassette chromosome recombinase genes ccrA and ccrB. In the present work, we detected homologues of the ccr genes in Staphylococcus hominis type strain GIFU12263 (equivalent to ATCC 27844), which is susceptible to methicillin . Sequence determination revealed that the ccr homologues in S . hominis were type 1 ccr genes (ccrA1 and ccrB1) that were localized on a genetic element structurally very similar to SCCmec except for the absence of the methicillin-resistance gene, mecA. This genetic element had mosaic-like patterns of homology with extant SCCmec elements, and we designated it SCC12263 and considered it a type I staphylococcal cassette chromosome (SCC) . The ccrB1 gene identified in the S . hominis strain is the first type 1 ccrB gene discovered to retain its function through the excision process as judged by two criteria: (i) SCC12263 was spontaneously excised during cultivation of the strain and (ii) introduction of the S . hominis ccrB1 into an MRSA strain carrying a type I SCCmec whose ccrB1 gene is inactive generated SCCmec excisants at a high frequency . The existence of an SCC without a mec determinant is indicative of a staphylococcal site-specific mobile genetic element that serves as a vehicle of transfer for various genetic markers between staphylococcal species .
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