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Polymorphic Mutation Frequencies in Escherichia coli: Emergence of Weak Mutators in Clinical Isolates. María-Rosario Baquero, 2004.Polymorphisms in the rifampin resistance mutation frequency (f) were studied in 696 Escherichia coli strains from Spain, Sweden, and Denmark . Of the 696 strains, 23% were weakly hypermutable (4 x 10–8 
f < 4 x 10–7), and 0.7%
were strongly hypermutable (f
4 x 10–7) . Weak mutators were
apparently more frequent in southern Europe and in blood isolates
(38%) than in urinary tract isolates (25%) and feces of healthy
volunteers (11%) .
Phenotypic Selection and Phase Variation Occur during Alfalfa Root Colonization by Pseudomonas fluorescens F113. María Sánchez-Contreras, 2002. Disparate Oxygen Responsiveness of Two Regulatory Cascades That Control Expression of Symbiotic Genes in Bradyrhizobium japonicum. Michel-Angelo Sciotti, 2003.Two oxygen-responsive regulatory systems controlling numerous symbiotic genes in Bradyrhizobium japonicum were assayed in free-living cultures for their capacity to activate target genes under different oxygen conditions . NifA- and FixLJ-controlled target genes showed disparate relative expression patterns . Induction of NifA-dependent genes was observed only at oxygen concentrations below 2% in the gas phase, whereas that of FixLJ-controlled targets progressively increased when the oxygen concentration was lowered from 21 to 5, 2, or 0.5% . We propose that this reflects a response to a gradient of increasing oxygen deprivation as bacteria invade their host during root nodule development . Additional Targets of the Bacillus subtilis Global Regulator CodY Identified by Chromatin Immunoprecipitation and Genome-Wide Transcript Analysis. Virginie Molle, 2003.Additional targets of CodY, a GTP-activated repressor of early stationary-phase genes in Bacillus subtilis, were identified by combining chromatin immunoprecipitation, DNA microarray hybridization, and gel mobility shift assays . The direct targets of CodY newly identified by this approach included regulatory genes for sporulation, genes that are likely to encode transporters for amino acids and sugars, and the genes for biosynthesis of branched-chain amino acids .
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