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Genetic Characterization of a Multicomponent Signal Transduction System Controlling the Expression of Cable Pili in Burkholderia cenocepacia. Mladen Tomich, 2004.Cable pili are peritrichous organelles expressed by certain strains of Burkholderia cenocepacia, believed to facilitate colonization of the lower respiratory tract in cystic fibrosis patients . The B . cenocepacia cblBACDS operon encodes the structural and accessory proteins required for the assembly of cable pili, as well as a gene designated cblS, predicted to encode a hybrid sensor kinase protein of bacterial two-component signal transduction systems . In this study we report the identification of two additional genes, designated cblT and cblR, predicted to encode a second hybrid sensor kinase and a response regulator, respectively . Analyses of the deduced amino acid sequences of the cblS and cblT gene products revealed that both putative sensor kinases have transmitter and receiver domains and that the cblT gene product has an additional C-terminal HPt domain . Mutagenesis of the cblS, cblT, or cblR gene led to a block in expression of CblA, the major pilin subunit, and a severe decrease in cblA transcript abundance . Using transcriptional fusion analyses, the decrease in the abundance of the cblA transcript in the cblS, cblT, and cblR mutants was shown to be due to a block in transcription from the cblB-proximal promoter, located upstream of the cblBACDS operon . Furthermore, ectopic expression of either cblS or cblR in wild-type B . cenocepacia strain BC7 led to a significant increase, while ectopic expression of cblT resulted in a dramatic decrease, in abundance of the CblA major pilin and the cblA transcript . Our results demonstrate that the B . cenocepacia cblS, cblT, and cblR genes are essential for cable pilus expression and that their effect is exerted at the level of transcription of the cblBACDS operon . These findings are consistent with the proposed function of the cblSTR gene products as a multicomponent signal transduction pathway controlling the expression of cable pilus biosynthetic genes in B . cenocepacia . Aquaporin Z of Escherichia coli: Reassessment of Its Regulation and Physiological Role. Eric Soupene, 2002.Transcription of an aqpZ-lac fusion in a single copy on the Escherichia coli chromosome increased as cells entered the stationary growth phase . This was true in a variety of media, and increased transcription in enriched medium required the RpoS sigma factor . Expression of the aqpZ-lac fusion was not affected by up- or downshifts in osmolality . Disruption of aqpZ had no detectable adverse effects . Molecular Diversity of Denitrifying Genes in Continental Margin Sediments within the Oxygen-Deficient Zone off the Pacific Coast of Mexico. Xueduan Liu, 2003.To understand the composition and structure of denitrifying communities in the oxygen-deficient zone off the Pacific coast of Mexico, the molecular diversity of nir genes from sediments obtained at four stations was examined by using a PCR-based cloning approach . A total of 50 operational taxonomic units (OTUs) for nirK and 82 OTUs for nirS were obtained from all samples . Forty-four of the nirS clones and 31 of the nirK clones were sequenced; the levels of similarity of the nirS clones were 52 to 92%, and the levels of similarity of the nirS clones were 50 to 99% . The percentages of overlapping OTUs between stations were 18 to 30% for nirS and 5 to 8% for nirK . Sequence analysis revealed that 26% of the nirS clones were related to the nirS genes of Alcaligenes faecalis (80 to 94% similar) and Pseudomonas stutzeri (80 to 99%), whereas 3 to 31% of the nirK clones were closely related to the nirK genes of Pseudomonas sp . strain G-179 (98 to 99%), Bradyrhizobium japonicum (91%), Blastobacter denitrificans (83%), and Alcaligenes xylosoxidans (96%) . The rest of the clones, however, were less than 80% similar to nirS and nirK sequences available in sequence databases . The results of a principal-component analysis (PCA) based on the percentage of OTUs and biogeochemical data indicated that the nitrate concentration and oxygen have an effect on the denitrifying communities . The communities at the stations in oxygen-deficient zones were more similar than the communities at the stations in the oxygenated zone . The denitrifying communities were more similar at the stations that were closer together and had similar nitrate levels . Also, the results of PCA based on biogeochemical properties suggest that geographic location and biogeochemical conditions, especially the nitrate and oxygen levels, appear to be the key factors that control the structure of denitrifying communities .
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