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Evidence of bar Minigene Expression and tRNA2IleSequestration as Peptidyl-tRNA2Ileduring Lambda Bacteriophage Development. Norma Angélica Oviedo de Anda, 2004.Lambda bacteriophage development is impaired in Escherichia coli cells defective for peptidyl (pep)-tRNA hydrolase (Pth) . Single-base-pair mutations (bar–) that affect translatable two-codon open reading frames named bar minigenes (barI or barII) in the lambda phage genome promote the development of this phage in Pth-defective cells (rap cells) . When the barI minigene is cloned and overexpressed from a plasmid, it inhibits protein synthesis and cell growth in rap cells by sequestering 
as
 .
Either
or Pth may reverse these effects . In this paper we present evidence
that both barI and barII minigenes are translatable elements
that sequester
as
.
In addition, overexpression of the barI minigene impairs the development
even of bar– phages in rap cells . Interestingly, tRNA
or Pth may reestablish lambda phage development . These results
suggest that lambda bar minigenes are expressed and
is sequestered as
during lambda phage development .
Regulation of the N-Acyl Homoserine Lactone-Dependent Quorum-Sensing System in Rhizosphere Pseudomonas putida WCS358 and Cross-Talk with the Stationary-Phase RpoS Sigma Factor and the Global Regulator GacA. Iris Bertani, 2004.Quorum sensing is a cell population-density dependent regulatory system which in gram-negative bacteria often involves the production and detection of N-acyl homoserine lactones (AHLs) . Some Pseudomonas putida strains have been reported to produce AHLs, and one quorum-sensing locus has been identified . However, it appears that the majority of strains do not produce AHLs . In this study we report the identification and regulation of the AHL-dependent system of rhizosphere P . putida WCS358 . This system is identical to the recently identified system of P . putida strain IsoF and very similar to the las system of Pseudomonas aeruginosa . It is composed of three genes, the luxI family member ppuI, the putative repressor rsaL, and the luxR family member ppuR . A genomic ppuR::Tn5 mutant of strain WCS358 was identified by its inability to produce AHLs when it was cross-streaked in close proximity to an AHL biosensor, whereas an rsaL::Tn5 genomic mutant was identified by its ability to overproduce AHL molecules . Using transcriptional promoter fusions, we studied expression profiles of the rsaL, ppuI, and ppuR promoters in various genetic backgrounds . At the onset of the stationary phase, the autoinducer synthase ppuI gene expression is under positive regulation by PpuR-AHL and under negative regulation by RsaL, indicating that the molecules could be in competition for binding at the ppuI promoter . In genomic rsaL::Tn5 mutants ppuI expression and production of AHL levels increased dramatically; however, both processes were still under growth phase regulation, indicating that RsaL is not involved in repressing AHL production at low cell densities . The roles of the global response regulator GacA and the stationary-phase sigma factor RpoS in the regulation of the AHL system at the onset of the stationary phase were also investigated . The P . putida WCS358 gacA gene was cloned and inactivated in the genome . It was determined that the three global regulatory systems are closely linked, with quorum sensing and RpoS regulating each other and GacA positively regulating ppuI expression . Studies of the regulation of AHL quorum-sensing systems have lagged behind other studies and are important for understanding how these systems are integrated into the overall growth phase and metabolic status of the cells . Single-Cell Protein Profiling of Wastewater Enterobacterial Communities Predicts Disinfection Efficiency. Gomathinayagam Ponniah, 2003.The efficiency of enterobacterial disinfection is dependent largely on enterobacterial community physiology . However, the relationship between enterobacterial community physiology and wastewater processing is unclear . The purpose of this study was to investigate this relationship . The influence of wastewater treatment processes on enterobacterial community physiology was examined at the single-cell level by using culture-independent methods . Intracellular concentrations of two conserved proteins, the growth-related protein Fis and the stationary-phase protein Dps, were analyzed by epifluoresence microscopy of uncultivated cells by using enterobacterial group-specific polyclonal fluorochrome-coupled antibodies . Enterobacterial single-cell community protein profiles were distinct for different types of biological treatment . The differences were not apparent when bulk methods of protein analysis were used . Trickling filter wastewater yielded Fis-enriched communities compared to the communities in submerged aeration basin wastewater . Community differences in Fis and Dps contents were used to predict disinfection efficiency . Disinfection of community samples by heat exposure combined with cultivation in selective media confirmed that enterobacterial communities exhibited significant differences in sensitivity to disinfection . These findings provide strategies that can be used to increase treatment plant performance, reduce the enterobacterial content in municipal wastewater, and minimize the release of disinfection by-products into receiving water .
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