Analysis Of Structural Variation Of Super Integron In Toxigenic O1 El Tor Vibrio Cholerae And Transcription Analysis Of Si In Different Conditions

Cholera is still an important public health challenge in many developing countries. Vibrio cholerae is the causative agent of cholera. Super-integron (SI) was found firstly in El Tor V. cholerae strain N16961 in 1999. Most of the gene functions in the SI remain unknown except that a few genes were related to the adaption of V. cholerae. Previous study indicated that substantial diversity existed in V. cholerae of different biotype. And the diversity of SI contributed largely to the difference between toxigenic El Tor strains. In this study, by employing PCR scanning and fragment sequencing, the structure of SI in 60 toxigenic V. cholerae isolated in different cholera epidemics between 1961 and 2008 in China were determined. Transcription analysis of the ORFs in SI in bile salt media, M9 media and AKI media were performed and compared to that in LB.The conservative and variant sites of Vibrio cholera repeat (VCR), the distribution and structure of VCR in N16961 were determined with BLAST, Artemis Comparison Tool, Clustal W and MEGA 4.0.The structure contents of the SI in 60 toxigenic V. cholerae isolated in 19 regions were analyzed and the structure maps of the tested strains were drawn. The structural variance of SIs was obvious among the different decades'epidemics, whereas the divergence was based on syntenic structure of SIs in these El Tor strains. Some variances were found, including insertions, replacements and most likely deletions by the recombination of repeat sequence and VCRs, and most of which clustered together. The SIs of the strains isolated in the 1960s and 1970s showed the much more diversity, whereas SI cassettes variation of strains of 1990s and after was much lower, with an～24kb deletion of signature, indicating the predominant SI in the host during different epidemics of years. The insertion cassettes suggested the mobilization from the SIs of other of V. cholerae serogroups and V. mimicus. The structure of the SIs in different cholera epidemic strains exhibited an obviously simplification trend. The study shows the efficiency of PCR Scanning combined with fragment sequencing in the cassette content construction of SIs in the toxigenic V. cholerae O1 strains, and the continuing cassettes flows in the SIs during the cholera pandemic.The comparison of the transcription of the ORFs in SI of N16961 grown in LB media to those in bile salt media, M9 media and AKI media were performed. The results indicated that some of the ORFs' transcription changed in bile salt media and in AKI media. Most of the ORFs'transcriptions were up-regulated while the strain was grown in M9 media. A small number of known function of ORF, mainly concentrated in the metabolism and Mobile and extrachromosomal element in the three medium, the expression of the ORFs about DNA metabolism and Fatty acid and phospholipid metabolism also appear in the SI with M9 culture condition, Hence we speculated that most of the functions of the ORFs in SI were related to the adaptive survival of V. cholerae at low nutritional status.