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Alcohol-Induced Delay of Viability Loss in Stationary-Phase Cultures of Escherichia coli. Marin Vuli, 2002.During prolonged incubation in stationary phase Escherichia coli undergoes starvation-induced differentiation, resulting in highly resistant cells . In rich medium with high amino acid content further incubation of cultures at high cell density leads to the generation of a population of cells no longer able to form colonies . The viability loss is due to some component of spent medium, active at high pH and high cell density, and can be prevented either by keeping the pH close to neutrality, by washing off the nonsalt components of the medium, or by keeping the saturating cell density low . Exposure to short-chain n-alcohols within a specific time window in stationary phase also prevents viability loss, in an rpoS-dependent fashion . The development of stress resistance, a hallmark of stationary-phase cells, is affected following alcohol treatment, as is the response to extracellular factors in spent medium . Alcohols seem to block cells in an early phase of starvation-induced differentiation, most likely by interfering with processes important for regulation of  s such as cell density signals and sensing the nutrient content of the medium .
A CheW Homologue Is Required for Myxococcus xanthus Fruiting Body Development, Social Gliding Motility, and Fibril Biogenesis. Kristen Bellenger, 2002.In bacteria with multiple sets of chemotaxis genes, the deletion of homologous genes or even different genes in the same operon can result in disparate phenotypes . Myxococcus xanthus is a bacterium with multiple sets of chemotaxis genes and/or homologues . It was shown previously that difA and difE, encoding homologues of the methyl-accepting chemoreceptor protein (MCP) and the CheA kinase, respectively, are required for M . xanthus social gliding (S) motility and development . Both difA and difE mutants were also defective in the biogenesis of the cell surface appendages known as extracellular matrix fibrils . In this study, we investigated the roles of the CheW homologue encoded by difC, a gene at the same locus as difA and difE . We showed that difC mutations resulted in defects in M . xanthus developmental aggregation, sporulation, and S motility . We demonstrated that difC is indispensable for wild-type cellular cohesion and fibril biogenesis but not for pilus production . We further illustrated the ectopic complementation of a difC in-frame deletion by a wild-type difC . The identical phenotypes of difA, difC, and difE mutants are consistent and supportive of the hypothesis that the Dif chemotaxis homologues constitute a chemotaxis-like signal transduction pathway that regulates M . xanthus fibril biogenesis and S motility . Spontaneously Arising mutL Mutators in Evolving Escherichia coli Populations Are the Result of Changes in Repeat Length. Aaron C. Shaver, 2003.Over the course of thousands of generations of growth in a glucose-limited environment, 3 of 12 experimental populations of Escherichia coli spontaneously and independently evolved greatly increased mutation rates . In two of the populations, the mutations responsible for this increased mutation rate lie in the same region of the mismatch repair gene mutL . In this region, a 6-bp repeat is present in three copies in the gene of the wild-type ancestor of the experimental populations but is present in four copies in one of the experimental populations and two copies in the other . These in-frame mutations either add or delete the amino acid sequence LA in the MutL protein . We determined that the replacement of the wild-type sequence with either of these mutations was sufficient to increase the mutation rate of the wild-type strain to a level comparable to that of the mutator strains . Complementation of strains bearing the mutator mutations with wild-type copies of either mutL or the mismatch repair gene uvrD rescued the wild-type mutation rate . The position of the mutator mutations—in the region of MutL known as the ATP lid—suggests a possible deficiency in MutL's ATPase activity as the cause of the mutator phenotype . The similarity of the two mutator mutations (despite the independent evolutionary histories of the populations that gave rise to them) leads to a discussion of the potential adaptive role of DNA repeats . Survival of Yersinia pestis on Environmental Surfaces. Laura J. Rose, 2003.The survival of two strains of Yersinia pestis (avirulent A1122 and virulent Harbin) on the surfaces of four materials was investigated . Viability was evaluated with epifluorescence microscopy by using the metabolic stain cyanoditolyl tetrazolium chloride and plate counts . Small numbers of cells suspended in phosphate buffer survived 2 to 4 h after visible drying on stainless steel, polyethylene, or glass and beyond 48 h on paper . Cells suspended in brain heart infusion broth (BHI) persisted more than 72 h on stainless steel, polyethylene, and glass . Small numbers of cells suspended in BHI were still viable at 120 h on paper . These data suggest that Y . pestis maintains viability for extended periods (last measured at 5 days) under controlled conditions .
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