Vibrio cholerae(V. cholerae) genome is equipped with a number of integrative mobile genetic element(IMGE) like prophages, plasmids, transposons or genomic islands, which provides fitness factors that help the pathogen...Vibrio cholerae(V. cholerae) genome is equipped with a number of integrative mobile genetic element(IMGE) like prophages, plasmids, transposons or genomic islands, which provides fitness factors that help the pathogen to survive in changing environmental conditions. Metagenomic analyses of clinical and environmental V. cholerae isolates revealed that dimer resolution sites(dif) harbor several structurally and functionally distinct IMGEs. All IMGEs present in the dif region exploit chromosomally encoded tyrosine recombinases, Xer C and Xer D, for integration. Integration takes place due to site-specific recombination between two specific DNA sequences; chromosomal sequence is called att B and IMGEs sequence is called att P. Different IMGEs present in the att P region have different attP structure but all of them are recognized by Xer C and Xer D enzymes and mediate either reversible or irreversible integration. Cholera toxin phage(CTXΦ), a lysogenic filamentous phage carrying the cholera toxin genes ctx AB, deserves special attention because it provides V. cholerae the crucial toxin and is always present in the dif region of all epidemic cholera isolates. Therefore, understanding the mechanisms of integration and dissemination of CTXΦ, genetic and ecological factors which support CTXΦ integration as well as production of virion from chromosomally integrated phage genome and interactions of CTXΦ with other genetic elements present in the genomes of V. cholerae is important for learning more about the biology of cholera pathogen.展开更多
A mercury biosensor was constructed by integrating biosensor genetic elements into E. coli JM109 chromosome in a single copy number, using the attP/attB recombination mechanism of λ phage. The genetic elements used i...A mercury biosensor was constructed by integrating biosensor genetic elements into E. coli JM109 chromosome in a single copy number, using the attP/attB recombination mechanism of λ phage. The genetic elements used include a regulatory protein gene （merR） along with operator/promoter （O/P） derived from the mercury resistance operon from pDU1358 plasmid of Serratia marcescens. The expression of reporter gene gfp is also controlled by merR/O/P. Integration of the construct into the chromosome was done to increase the stability and precision of the biosensor. This biosensor could detect Hg（Ⅱ） ions in the concentration range of 100–1700 nmol/L, and manifest the result as the expression of GFP. The GFP expression was significantly different （P 0.05） for each concentration of inducing Hg（Ⅱ） ions in the detection range, which reduces the chances of misinterpretation of results. A model using regression method was also derived for the quantification of the concentration of Hg（Ⅱ） in water samples.展开更多
基金Supported by Research in the Laboratory of Das B and NairGB is funded in part by Department of Science Technology,No.SB/FT/LS-309/2012Government of India(GOI)and the Department of Biotechnology,No.BT/MB/THSTI/HMC-SFC/2011Research in the Laboratory of Bhadra RK is partly financiallysupported by Council of Scientific and Industrial Research,GOIand Indian Council of Medical Research,GOI
文摘Vibrio cholerae(V. cholerae) genome is equipped with a number of integrative mobile genetic element(IMGE) like prophages, plasmids, transposons or genomic islands, which provides fitness factors that help the pathogen to survive in changing environmental conditions. Metagenomic analyses of clinical and environmental V. cholerae isolates revealed that dimer resolution sites(dif) harbor several structurally and functionally distinct IMGEs. All IMGEs present in the dif region exploit chromosomally encoded tyrosine recombinases, Xer C and Xer D, for integration. Integration takes place due to site-specific recombination between two specific DNA sequences; chromosomal sequence is called att B and IMGEs sequence is called att P. Different IMGEs present in the att P region have different attP structure but all of them are recognized by Xer C and Xer D enzymes and mediate either reversible or irreversible integration. Cholera toxin phage(CTXΦ), a lysogenic filamentous phage carrying the cholera toxin genes ctx AB, deserves special attention because it provides V. cholerae the crucial toxin and is always present in the dif region of all epidemic cholera isolates. Therefore, understanding the mechanisms of integration and dissemination of CTXΦ, genetic and ecological factors which support CTXΦ integration as well as production of virion from chromosomally integrated phage genome and interactions of CTXΦ with other genetic elements present in the genomes of V. cholerae is important for learning more about the biology of cholera pathogen.
基金Director, Central Institute of Fisheries Education, Mumbaifor providing facility and financial assistance in the form of Masters’ Fellowship during the research period
文摘A mercury biosensor was constructed by integrating biosensor genetic elements into E. coli JM109 chromosome in a single copy number, using the attP/attB recombination mechanism of λ phage. The genetic elements used include a regulatory protein gene （merR） along with operator/promoter （O/P） derived from the mercury resistance operon from pDU1358 plasmid of Serratia marcescens. The expression of reporter gene gfp is also controlled by merR/O/P. Integration of the construct into the chromosome was done to increase the stability and precision of the biosensor. This biosensor could detect Hg（Ⅱ） ions in the concentration range of 100–1700 nmol/L, and manifest the result as the expression of GFP. The GFP expression was significantly different （P 0.05） for each concentration of inducing Hg（Ⅱ） ions in the detection range, which reduces the chances of misinterpretation of results. A model using regression method was also derived for the quantification of the concentration of Hg（Ⅱ） in water samples.
