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The PmrA-Regulated pmrC Gene Mediates Phosphoethanolamine Modification of Lipid A and Polymyxin Resistance in Salmonella enterica. Hyunwoo Lee, 2004.The PmrA/PmrB regulatory system of Salmonella enterica controls the modification of lipid A with aminoarabinose and phosphoethanolamine . The aminoarabinose modification is required for resistance to the antibiotic polymyxin B, as mutations of the PmrA-activated pbg operon or ugd gene result in strains that lack aminoarabinose in their lipid A molecules and are more susceptible to polymyxin B . Additional PmrA-regulated genes appear to participate in polymyxin B resistance, as pbgP and ugd mutants are not as sensitive to polymyxin B as a pmrA mutant . Moreover, the role that the phosphoethanolamine modification of lipid A plays in the resistance to polymyxin B has remained unknown . Here we address both of these questions by establishing that the PmrA-activated pmrC gene encodes an inner membrane protein that is required for the incorporation of phosphoethanolamine into lipid A and for polymyxin B resistance . The PmrC protein consists of an N-terminal region with five transmembrane domains followed by a large periplasmic region harboring the putative enzymatic domain . A pbgP pmrC double mutant resembled a pmrA mutant both in its lipid A profile and in its susceptibility to polymyxin B, indicating that the PmrA-dependent modification of lipid A with aminoarabinose and phosphoethanolamine is responsible for PmrA-regulated polymyxin B resistance . Emergence and Spread of Three Clonally Related Virulent Isolates of CTX-M-15-Producing Escherichia coli with Variable Resistance to Aminoglycosides and Tetracycline in a French Geriatric Hospital. Véronique Leflon-Guibout, 2004.Three types of multidrug-resistant Escherichia coli isolates, called GEN S, GEN R, and AMG S, according to their three different aminoglycoside resistance patterns, were responsible for urinary tract colonization or infection in 87, 12, and 13 new patients, respectively, in a French 650-bed geriatric hospital over a 13-month period . The three E . coli types belonged to the same clone and phylogenetic group (group B2) and had identical transferable plasmid contents (a 120-kb plasmid), ß-lactam and fluoroquinolone resistance genotypes (blaTEM-1B, blaCTX-M-15, and double mutations in both the gyrA and the parC genes), and virulence factor genotypes (aer, fyuA, and irp2) . They disseminated in the geriatric hospital, where the antibiotics prescribed most often were fluoroquinolones and ceftriaxone, but not in the affiliated acute-care hospital, where isolation precautions were applied to the transferred patients . Thus, E . coli isolates, both CTX-M-type ß-lactamase producers and fluoroquinolone-resistant isolates, might present a new challenge for French health care settings . Genomewide Transcriptional Analysis of the Cold Shock Response in Bacillus subtilis. Carsten L. Beckering, 2002.Previous studies with two-dimensional gel electrophoresis techniques revealed that the cold shock response in Bacillus subtilis is characterized by rapid induction and accumulation of two classes of specific proteins, which have been termed cold-induced proteins (CIPs) and cold acclimatization proteins (CAPs), respectively . Only recently, the B . subtilis two-component system encoded by the desKR operon has been demonstrated to be essential for the cold-induced expression of the lipid-modifying desaturase Des, which is required for efficient cold adaptation of the membrane in the absence of isoleucine . At present, one of the most intriguing questions in this research field is whether DesKR plays a global role in cold signal perception and transduction in B . subtilis . In this report, we present the first genomewide transcriptional analysis of a cold-exposed bacterium and demonstrate that the B . subtilis two-component system DesKR exclusively controls the desaturase gene des and is not the cold-triggered regulatory system of global relevance . In addition to this, we identified a set of genes that might participate as novel players in the cold shock adaptation of B . subtilis . Two cold-induced genes, the elongation factor homolog ylaG and the  L-dependent transcriptional activator homolog yplP, have been examined by construction and analysis of deletion mutants .
Expression of a Cloned Cyclopropane Fatty Acid Synthase Gene Reduces Solvent Formation in Clostridium acetobutylicum ATCC 824. Yinsuo Zhao, 2003.The cyclopropane fatty acid synthase gene (cfa) of Clostridium acetobutylicum ATCC 824 was cloned and overexpressed under the control of the clostridial ptb promoter . The function of the cfa gene was confirmed by complementation of an Escherichia coli cfa-deficient strain in terms of fatty acid composition and growth rate under solvent stress . Constructs expressing cfa were introduced into C . acetobutylicum hosts and cultured in rich glucose broth in static flasks without pH control . Overexpression of the cfa gene in the wild type and in a butyrate kinase-deficient strain increased the cyclopropane fatty acid content of early-log-phase cells as well as initial acid and butanol resistance . However, solvent production in the cfa-overexpressing strain was considerably decreased, while acetate and butyrate levels remained high . The findings suggest that overexpression of cfa results in changes in membrane properties that dampen the full induction of solventogenesis . The overexpression of a marR homologous gene preceding the cfa gene in the clostridial genome resulted in reduced cyclopropane fatty acid accumulation .
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