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Traffic at the tmRNA Gene. Kelly P. Williams, 2003.A partial screen for genetic elements integrated into completely sequenced bacterial genomes shows more significant bias in specificity for the tmRNA gene (ssrA) than for any type of tRNA gene . Horizontal gene transfer, a major avenue of bacterial evolution, was assessed by focusing on elements using this single attachment locus . Diverse elements use ssrA; among enterobacteria alone, at least four different integrase subfamilies have independently evolved specificity for ssrA, and almost every strain analyzed presents a unique set of integrated elements . Even elements using essentially the same integrase can be very diverse, as is a group with an ssrA-specific integrase of the P4 subfamily . This same integrase appears to promote damage routinely at attachment sites, which may be adaptive . Elements in arrays can recombine; one such event mediated by invertible DNA segments within neighboring elements likely explains the monophasic nature of Salmonella enterica serovar Typhi . One of a limited set of conserved sequences occurs at the attachment site of each enterobacterial element, apparently serving as a transcriptional terminator for ssrA . Elements were usually found integrated into tRNA-like sequence at the 3' end of ssrA, at subsites corresponding to those used in tRNA genes; an exception was found at the non-tRNA-like 3' end produced by ssrA gene permutation in cyanobacteria, suggesting that, during the evolution of new site specificity by integrases, tropism toward a conserved 3' end of an RNA gene may be as strong as toward a tRNA-like sequence . The proximity of ssrA and smpB, which act in concert, was also surveyed . Microbiological Evaluation of a Range of Disinfectant Products To Control Mixed-Species Biofilm Contamination in a Laboratory Model of a Dental Unit Water System. J. T. Walker, 2003.Dental unit water system (DUWS) tubing harbors complex multispecies biofilms that are responsible for high microbial levels at the distal outlet . The aim of this study was to use an established biofilm laboratory model to simulate biofouling of DUWS to evaluate practical, cost-effective, and evidence-based methods of microbial decontamination . Reproducible biofilms were developed in the model over 14 days; decontamination was assessed using total viable counts (TVC) and microscopic-image analysis techniques to view the inner surface of tubing . Flushing did not reduce the biofilm coverage or TVC . Combizyme and ozone did not completely eliminate the viable bacteria (70 and 65% reduction in biofilm TVC, respectively), nor did they remove the biofilm (45 and 57% reduction in biofilm coverage, respectively) . Chlorhexidine and Bio2000 (active agent: ethanol and chlorhexidine), Tegodor and Gigasept Rapid (aldehyde based), and Grotanol (hydroxide based) completely eliminated the TVC but did not completely remove biofilm (31, 53 33, 34, and 64.9% reduction of biofilm coverage, respectively) . Other products including Grotanol Flussig (phenol based), Betadine (povidone-iodine based), Alpron (chlorite based), and the hydroxide-containing products Sporklenz, Sterilex Ultra, Dialox, Sterilox, Sanosil, Oxigenal, and Grotanat Bohrerbad resulted in a 100% reduction in the biofilm TVC and a >95% reduction in biofilm coverage . The study demonstrated that while many disinfectants achieve a sufficient reduction in TVC they may not necessarily remove unwanted biofilm from the tubing surfaces as tested in this laboratory-controlled biofilm model . Immobilization of Arsenite and Ferric Iron by Acidithiobacillus ferrooxidans and Its Relevance to Acid Mine Drainage. K. Duquesne, 2003.Weathering of the As-rich pyrite-rich tailings of the abandoned mining site of Carnoulès (southeastern France) results in the formation of acid waters heavily loaded with arsenic . Dissolved arsenic present in the seepage waters precipitates within a few meters from the bottom of the tailing dam in the presence of microorganisms . An Acidithiobacillus ferrooxidans strain, referred to as CC1, was isolated from the effluents . This strain was able to remove arsenic from a defined synthetic medium only when grown on ferrous iron . This A . ferrooxidans strain did not oxidize arsenite to arsenate directly or indirectly . Strain CC1 precipitated arsenic unexpectedly as arsenite but not arsenate, with ferric iron produced by its energy metabolism . Furthermore, arsenite was almost not found adsorbed on jarosite but associated with a poorly ordered schwertmannite . Arsenate is known to efficiently precipitate with ferric iron and sulfate in the form of more or less ordered schwertmannite, depending on the sulfur-to-arsenic ratio . Our data demonstrate that the coprecipitation of arsenite with schwertmannite also appears as a potential mechanism of arsenite removal in heavily contaminated acid waters . The removal of arsenite by coprecipitation with ferric iron appears to be a common property of the A . ferrooxidans species, as such a feature was observed with one private and three collection strains, one of which was the type strain .
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