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Identification of Operators and Promoters That Control SXT Conjugative Transfer. John W. Beaber, 2004.Transfer of SXT, a Vibrio cholerae-derived integrating conjugative element that encodes multiple antibiotic resistance genes, is repressed by SetR, a  434
cI-related repressor . Here we identify divergent promoters
between s086 and setR that drive expression of the
regulators of SXT transfer . One transcript encodes the activators of
transfer, setC and setD . The second transcript codes
for SetR and, like the cI transcript of lambda, is leaderless .
SetR binds to four operators located between setR and s086;
the locations and relative affinities of these sites suggest a
model for regulation of SXT transfer .
Membrane Restructuring by Bordetella pertussis Adenylate Cyclase Toxin, a Member of the RTX Toxin Family. César Martín, 2004.Adenylate cyclase toxin (ACT) is secreted by Bordetella pertussis, the bacterium causing whooping cough . ACT is a member of the RTX (repeats in toxin) family of toxins, and like other members in the family, it may bind cell membranes and cause disruption of the permeability barrier, leading to efflux of cell contents . The present paper summarizes studies performed on cell and model membranes with the aim of understanding the mechanism of toxin insertion and membrane restructuring leading to release of contents . ACT does not necessarily require a protein receptor to bind the membrane bilayer, and this may explain its broad range of host cell types . In fact, red blood cells and liposomes (large unilamellar vesicles) display similar sensitivities to ACT . A varying liposomal bilayer composition leads to significant changes in ACT-induced membrane lysis, measured as efflux of fluorescent vesicle contents . Phosphatidylethanolamine (PE), a lipid that favors formation of nonlamellar (inverted hexagonal) phases, stimulated ACT-promoted efflux . Conversely, lysophosphatidylcholine, a micelle-forming lipid that opposes the formation of inverted nonlamellar phases, inhibited ACT-induced efflux in a dose-dependent manner and neutralized the stimulatory effect of PE . These results strongly suggest that ACT-induced efflux is mediated by transient inverted nonlamellar lipid structures . Cholesterol, a lipid that favors inverted nonlamellar phase formation and also increases the static order of phospholipid hydrocarbon chains, among other effects, also enhanced ACT-induced liposomal efflux . Moreover, the use of a recently developed fluorescence assay technique allowed the detection of trans-bilayer (flip-flop) lipid motion simultaneous with efflux . Lipid flip-flop further confirms the formation of transient nonlamellar lipid structures as a result of ACT insertion in bilayers . National Surveillance of Methicillin-Resistant Staphylococcus aureus in Belgian Hospitals Indicates Rapid Diversification of Epidemic Clones. Olivier Denis, 2004.Methicillin-resistant Staphylococcus aureus (MRSA) strains (n = 455) collected in 2001 from 100 Belgian hospitals were characterized by molecular typing and by resistance gene distribution to macrolides-lincosamides-streptogramins and to aminoglycoside antibiotics . Rapid diversification of MRSA clones, compared with results of previous surveys, was evidenced by the broad geographic distribution of seven major clones belonging to the pandemic MRSA clonal complexes 5, 8, 22, 30, and 45 by multilocus sequence typing . Resident Parking Only: Rhamnolipids Maintain Fluid Channels in Biofilms. Manuel Espinosa-Urgel, 2003. Detection of the Free-Living Forms of Sulfide-Oxidizing Gill Endosymbionts in the Lucinid Habitat (Thalassia testudinum Environment). Olivier Gros, 2003.Target DNA from the uncultivable Codakia orbicularis endosymbiont was PCR amplified from sea-grass sediment . To confirm that such amplifications originated from intact bacterial cells rather than free DNA, whole-cell hybridization (fluorescence in situ hybridization technique) with the specific probe Symco2 was performed along with experimental infection of aposymbiotic juveniles placed in contact with the same sediment . Taken together, the data demonstrate that the sulfide-oxidizing gill endosymbiont of Codakia orbicularis is present in the environment as a free-living uncultivable form .
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