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Identification of Residues of the Kid Toxin Involved in Autoregulation of the parD System. Marc Lemonnier, 2004.The toxin-antitoxin system parD (kis kid) of plasmid R1 is coregulated by the coordinated action of its two gene products . Here we describe the isolation and the in vivo characterization of three single-amino-acid changes in the Kid toxin, G4E, C74Y, and E91K, that affect the coregulatory activity but preserve the toxicity of the protein . The REP2 Repeats of the Genome of Neisseria meningitidis Are Associated with Genes Coordinately Regulated during Bacterial Cell Interaction. Sandrine Morelle, 2003.Interaction with host cells is essential in meningococcal pathogenesis especially at the blood-brain barrier . This step is likely to involve a common regulatory pathway allowing coordinate regulation of genes necessary for the interaction with endothelial cells . The analysis of the genomic sequence of Neisseria meningitidis Z2491 revealed the presence of many repeats . One of these, designated REP2, contains a -24/-12 type promoter and a ribosome binding site 5 to 13 bp before an ATG . In addition most of these REP2 sequences are located immediately upstream of an ORF . Among these REP2-associated genes are pilC1 and crgA, described as being involved in steps essential for the interaction of N . meningitidis with host cells . Furthermore, the REP2 sequences located upstream of pilC1 and crgA correspond to the previously identified promoters known to be induced during the initial localized adhesion of N . meningitidis with human cells . This characteristic led us to hypothesize that at least some of the REP2-associated genes were upregulated under the same circumstances as pilC1 and crgA . Quantitative PCR in real time demonstrated that the expression of 14 out of 16 REP2-associated genes were upregulated during the initial localized adhesion of N . meningitidis . Taken together, these data suggest that these repeats control a set of genes necessary for the efficient interaction of this pathogen with host cells . Subsequent mutational analysis was performed to address the role of these genes during meningococcus-cell interaction . PCR-Restriction Fragment Length Polymorphism Analysis of the Phospholipase B (PLB1) Gene for Subtyping of Cryptococcus neoformans Isolates. G. Nicolas Latouche, 2003.Cryptococcus neoformans is a pathogenic yeast that is currently divided into three varieties, five serotypes, and eight molecular types . The following report describes the use of PCR-restriction fragment length polymorphism (RFLP) analysis of the phospholipase B gene (PLB1) as a simple tool to differentiate between C . neoformans subgroups . A PLB1 fragment, 1,970 bp, was amplified and digested with either AvaI or HindIII . Both sets of profiles grouped the isolates into their respective varieties, but only the AvaI profiles allowed for the identification of the eight molecular types via the corresponding RFLP profiles A1 to A8 . Digestion of the same fragments with HindIII resulted in RFLP profiles H1 to H5, which distinguished only between serotype A, AD, D, and B/C . Neither enzyme distinguished serotype B from serotype C . The serotype AD profile was a composite of the serotype A and D profiles . Further investigation showed that the serotype AD isolates used in this study are heterozygous, with one allele of PLB1 originating from a serotype A parent and the other from a serotype D parent . Single-Leaf Resolution of the Temporal Population Dynamics of Aureobasidium pullulans on Apple Leaves. Scott T. Woody, 2003.The abundance of phylloplane microorganisms typically varies over several orders of magnitude among leaves sampled concurrently . Because the methods traditionally used to sample leaves are destructive, it has remained unclear whether this high variability is due to fixed differences in habitat quality among leaves or to asynchronous temporal variation in the microbial population density on individual leaves . We developed a novel semidestructive assay to repeatedly sample the same apple leaves from orchard trees over time by removing progressively more proximal  1-cm-wide transverse segments . Aureobasidium pullulans densities were determined by standard leaf homogenization and plating procedures and were expressed as CFU per square centimeter of segment . The A . pullulans population densities among leaves were lognormally distributed . The variability in A . pullulans population densities among subsections of a given leaf was one-third to one-ninth the variability among whole leaves harvested concurrently . Sequential harvesting of leaf segments did not result in detectable changes in A . pullulans density on residual leaf surfaces . These findings implied that we could infer whole-leaf A . pullulans densities over time by using partial leaves . When this successive sampling regimen was applied over the course of multiple 7- to 8-day experiments, the among-leaf effects were virtually always the predominant source of variance in A . pullulans density estimates . Changes in A . pullulans density tended to be synchronous among leaves, such that the rank order of leaves arrayed with respect to A . pullulans density was largely maintained through time . Occasional periods of asynchrony were observed, but idiosyncratic changes in A . pullulans density did not contribute appreciably to variation in the distribution of populations among leaves . This suggests that persistent differences in habitat (leaf) quality are primarily responsible for the variation in A . pullulans density among leaves in nature .
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