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Bacteriophage Tuc2009 Encodes a Tail-Associated Cell Wall-Degrading Activity. John G. Kenny, 2004.Tuc2009 is a P335-type member of the tailed-phage supergroup Siphoviridae and was originally identified as a resident prophage of the gram-positive bacterium Lactococcus lactis UC509 . A Tuc2009 gene designated tal2009 which is located within the morphogenic module was shown to specify a lytic activity within the 3' portion of its coding region . Comparative sequence analysis indicated that the cell wall-degrading part of Tal2009 is a member of the M37 protein family and that Tal2009 lacks a cell-binding domain, a finding supported by binding studies . Tal2009 appears to undergo self-mediated posttranslational processing in both L . lactis and Escherichia coli . Antibodies directed against a purified C-terminal portion of Tal2009 were used for immunoelectron microscopy, which showed that Tal2009 is located at the tail tip of Tuc2009 . Antibody neutralization studies demonstrated that Tal2009-directed antibodies inhibited the ability of phage to mediate host lysis by more than 100-fold . These data indicate that tal2009 encodes a tail-associated lysin involved in localized cell wall degradation, thus allowing the Tuc2009 DNA injection machinery access to the membrane of its bacterial host . Allelic Diversity and Population Structure in Vibrio cholerae O139 Bengal Based on Nucleotide Sequence Analysis. M. Farfán, 2002.Comparative analysis of gene fragments of six housekeeping loci, distributed around the two chromosomes of Vibrio cholerae, has been carried out for a collection of 29 V . cholerae O139 Bengal strains isolated from India during the first epidemic period (1992 to 1993) . A toxigenic O1 ElTor strain from the seventh pandemic and an environmental non-O1/non-O139 strain were also included in this study . All loci studied were polymorphic, with a small number of polymorphic sites in the sequenced fragments . The genetic diversity determined for our O139 population is concordant with a previous multilocus enzyme electrophoresis study in which we analyzed the same V . cholerae O139 strains . In both studies we have found a higher genetic diversity than reported previously in other molecular studies . The results of the present work showed that O139 strains clustered in several lineages of the dendrogram generated from the matrix of allelic mismatches between the different genotypes, a finding which does not support the hypothesis previously reported that the O139 serogroup is a unique clone . The statistical analysis performed in the V . cholerae O139 isolates suggested a clonal population structure . Moreover, the application of the Sawyer's test and split decomposition to detect intragenic recombination in the sequenced gene fragments did not indicate the existence of recombination in our O139 population . Plasmid DNA Supercoiling and Survival in Long-Term Cultures of Escherichia coli: Role of NaCl. Annie Conter, 2003.The relationship between the survival of Escherichia coli during long-term starvation in rich medium and the supercoiling of a reporter plasmid (pBR322) has been studied . In aerated continuously shaken cultures, E . coli lost the ability to form colonies earlier in rich NaCl-free Luria-Bertani medium than in NaCl-containing medium, and the negative supercoiling of plasmid pBR322 declined more rapidly in the absence of NaCl . Addition of NaCl at the 24th hour restored both viability and negative supercoiling in proportion to the concentration of added NaCl . Addition of ofloxacin, a quinolone inhibitor of gyrase, abolished rescue by added NaCl in proportion to the ofloxacin added . This observation raises the possibility that cells had the ability to recover plasmid supercoiling even if nutrients were not available and could survive during long-term starvation in a manner linked, at least in part, to the topological state of DNA and gyrase activity .
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