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Transposition of the Heat-Stable Toxin astA Gene into a Gifsy-2-Related Prophage of Salmonella enterica Serovar Abortusovis. Donatella Bacciu, 2004.The horizontal transfer and acquisition of virulence genes via mobile genetic elements have been a major driving force in the evolution of Salmonella pathogenicity . Serovars of Salmonella enterica carry variable assortments of phage-encoded virulence genes, suggesting that temperate phages play a pivotal role in this process . Epidemic isolates of S . enterica serovar Typhimurium are consistently lysogenic for two lambdoid phages, Gifsy-1 and Gifsy-2, carrying known virulence genes . Other serovars of S . enterica, including serovars Dublin, Gallinarum, Enteritidis, and Hadar, carry distinct prophages with similarity to the Gifsy phages . In this study, we analyzed Gifsy-related loci from S . enterica serovar Abortusovis, a pathogen associated exclusively with ovine infection . A cryptic prophage, closely related to serovar Typhimurium phage Gifsy-2, was identified . This element, named Gifsy-2AO, was shown to contribute to serovar Abortusovis systemic infection in lambs . Sequence analysis of the prophage b region showed a large deletion which covers genes encoding phage tail fiber proteins and putative virulence factors, including type III secreted effector protein SseI (GtgB, SrfH) . This deletion was identified in most of the serovar Abortusovis isolates tested and might be dependent on the replicative transposition of an adjacent insertion sequence, IS1414, previously identified in pathogenic Escherichia coli strains . IS1414 encodes heat-stable toxin EAST1 (astA) and showed multiple genomic copies in isolates of serovar Abortusovis . To our knowledge, this is the first evidence of intergeneric transfer of virulence genes via insertion sequence elements in Salmonella . The acquisition of IS1414 (EAST1) and its frequent transposition within the chromosome might improve the fitness of serovar Abortusovis within its narrow ecological niche . Roles of Internal Cysteines in the Function, Localization, and Reactivity of the TraV Outer Membrane Lipoprotein Encoded by the F Plasmid. Robin L. Harris, 2002.We have examined the functional role of two internal cysteine residues of the F-plasmid TraV outer membrane lipoprotein . Each was mutated to a serine separately and together to yield three mutant traV genes: traVC10S, traVC18S, and traVC10S/C18S . All three cysteine mutations complemented a traV mutant for DNA donor activity and for sensitivity to donor-specific bacteriophage; however, when measured by a transduction assay, the donor-specific DNA bacteriophage sensitivities of the traVC18S and, especially, traVC10S/C18S mutant strains were significantly less than those of the traV+ and traVC10S strains . Thus, unlike the Agrobacterium tumefaciens T-plasmid-encoded VirB7 outer membrane lipoprotein, TraV does not require either internal cysteine to retain significant biological activity . By Western blot analysis, all three mutant TraV proteins were shown to accumulate in the outer membrane . However, by nonreducing gel electrophoresis, wild-type TraV and especially the TraVC18S mutant were shown to form mixed disulfides with numerous cell envelope proteins . This was not observed with the TraVC10S or TraVC10S/C18S proteins . Thus, it appears that TraV C10 is unusually reactive and that this reactivity is reduced by C18, perhaps by intramolecular oxidation . Finally, whereas the TraVC10S and TraVC18S proteins fractionated primarily with the outer membrane, as did the wild-type protein, the TraVC10S/C18S protein was found in osmotic shock fluid and inner membrane fractions as well as outer membrane fractions . Hence, at least one cysteine is required for the efficient localization of TraV to the outer membrane . Isolation of a New Hemimethylated DNA Binding Protein Which Regulates dnaA Gene Expression. Emmanuelle d'Alençon, 2003.In this report, we show that yccV, a gene of unknown function, encodes a protein having an affinity for a hemimethylated oriC DNA and that the protein negatively controls dnaA gene expression in vivo . Impact of Seasonal Variations and Nutrient Inputs on Nitrogen Cycling and Degradation of Hexadecane by Replicated River Biofilms. Martin R. Chénier, 2003.Biofilm communities cultivated in rotating annular bioreactors using water from the South Saskatchewan River were assessed for the effects of seasonal variations and nutrient (C, N, and P) additions . Confocal laser microscopy revealed that while control biofilms were consistently dominated by bacterial biomass, the addition of nutrients shifted biofilms of summer and fall water samples to phototrophic-dominated communities . In nutrient-amended biofilms, similar patterns of nitrification, denitrification, and hexadecane mineralization rates were observed for winter and spring biofilms; fall biofilms had the highest rates of nitrification and hexadecane mineralization, and summer biofilms had the highest rates of denitrification . Very low rates of all measured activities were detected in control biofilms (without nutrient addition) regardless of season . Nutrient addition caused large increases in hexadecane mineralization and denitrification rates but only modest increases, if any, in nitrification rates, depending upon the season . Generally, both alkB and nirK were more readily PCR amplified from nutrient-amended biofilms . Both genes were amplified from all samples except for nirK from the fall control biofilm . It appears that bacterial production in the South Saskatchewan River water is limited by the availability of nutrients and that biofilm activities and composition vary with nutrient availability and time of year .
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