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H-NS Represses Salmonella enterica Serovar Typhimurium dsbA Expression during Exponential Growth. C. V. Gallant, 2004.Disulfide bond formation catalyzed by disulfide oxidoreductases occurs in the periplasm and plays a major role in the properfolding and integrity of many proteins . In this study, we wereinterested in elucidating factors that influence the regulationof dsbA, a gene coding for the primary disulfide oxidoreductasefound in Salmonella enterica serovar Typhimurium . Strains withmutations created by transposon mutagenesis were screened forstrains with altered expression of dsbA . A mutant [NLM2173]was found where maximal expression of a dsbA::lacZ transcriptional fusion occurred in the exponential growth phase in contrastto that observed in the wild type where maximal expression occursin stationary phase . Sequence analysis of NLM2173 demonstratedthat the transposon had inserted upstream of the gene encodingH-NS . Western immunoblot analysis using H-NS and StpA antibodiesshowed decreased amounts of H-NS protein in NLM2173, and thisreduction in H-NS correlated with an increase of StpA protein.Northern blot analysis with a dsbA-specific probe showed anincrease in dsbA transcript during exponential phase of growth.Direct binding of H-NS to the dsbA promoter region was verifiedusing purified H-NS in electrophoretic mobility shift assays.Thus, a reduction in H-NS protein is correlated with a derepressionof dsbA in NLM2173, suggesting that H-NS normally plays a rolein suppressing the expression of dsbA during exponential phasegrowth. Identification and Characterization of Two Temperature-Induced Surface-Associated Proteins of Streptococcus suis with High Homologies to Members of the Arginine Deiminase System of Streptococcus pyogenes. Nora Winterhoff, 2002.The present study was performed to identify stress-induced putative virulence proteins of Streptococcus suis . For this, protein expression patterns of streptococci grown at 32, 37, and 42°C were compared by one- and two-dimensional gel electrophoresis . Temperature shifts from 32 and 37 to 42°C induced expression of two cell wall-associated proteins with apparent molecular masses of approximately 47 and 53 kDa . Amino-terminal sequence analysis of the two proteins indicated homologies of the 47-kDa protein with an ornithine carbamoyltransferase (OCT) from Streptococcus pyogenes and of the 53-kDa protein with the streptococcal acid glycoprotein (SAGP) from S . pyogenes, an arginine deiminase (AD) recently proposed as a putative virulence factor . Cloning and sequencing the genes encoding the putative OCT and AD of S . suis, octS and adiS, respectively, revealed that they had 81.2 (octS) and 80.2% (adiS) identity with the respective genes of S . pyogenes . Both genes belong to the AD system, also found in other bacteria . Southern hybridization analysis demonstrated the presence of the adiS gene in all 42 serotype 2 and 9 S . suis strains tested . In 9 of these 42 strains, selected randomly, we confirmed expression of the AdiS protein, homologous to SAGP, by immunoblot analysis using a specific antiserum against the SAGP of S . pyogenes . In all strains AD activity was detected . Furthermore, by immunoelectron microscopy using the anti-S . pyogenes SAGP antiserum we were able to demonstrate that the AdiS protein is expressed on the streptococcal surface in association with the capsular polysaccharides but is not coexpressed with them . Phylogenetic Diversity, Abundance, and Axial Distribution of Bacteria in the Intestinal Tract of Two Soil-Feeding Termites (Cubitermes spp.). Dirk Schmitt-Wagner, 2003.The hindgut of soil-feeding termites is highly compartmentalized and characterized by pronounced axial dynamics of the intestinal pH and microbial processes such as hydrogen production, methanogenesis, and reductive acetogenesis . Nothing is known about the bacterial diversity and the abundance or axial distribution of the major phylogenetic groups in the different gut compartments . In this study, we showed that the variety of physicochemical conditions is reflected in the diversity of the microbial communities in the different gut compartments of two Cubitermes species (Termitidae: Termitinae) . 16S rRNA gene clones from the highly alkaline first proctodeal segment (P1) of Cubitermes orthognathus represented almost exclusively gram-positive bacteria with low G+C content (LGC bacteria) . In the posterior gut segments, their proportion decreased progressively, and the clone libraries comprised a variety of phyla, including the Cytophaga-Flexibacter-Bacteroides group, various subgroups of Proteobacteria, and the spirochetes . Phylogenetic analysis revealed that many of the clones clustered with sequences from the guts of other termites, and some even formed clusters containing only clones from C . orthognathus . The abundance and axial distribution of major phylogenetic groups in the gut of Cubitermes ugandensis were determined by fluorescence in situ hybridization with group-specific oligonucleotide probes . While the results were generally in good agreement with those of the clonal analysis, direct counts with probes specific for the Planctomycetales revealed a severe underestimation of representatives of this phylum in the clone libraries . Results obtained with newly designed FISH probes directed against two clusters of LGC clones from C . orthognathus indicated that the clones were restricted to specific gut regions . A molecular fingerprinting analysis published in a companion paper (D . Schmitt-Wagner, M . W . Friedrich, B . Wagner, and A . Brune, Appl . Environ . Microbiol . 69:6018-6024, 2003) corroborated the presence of compartment-specific bacterial communities in the gut of different Cubitermes species .
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