R-052. Dynamics of the Integron-Associated Mobile Gene Cassette Pool of a Natural Vibrio cholerae Population

Y. Boucher1, D. E. Hunt2, M. Labbate3, H. W. Stokes3, M. F. Polz1;
1Massachusetts Inst. of Technology, Cambridge, MA, 2Univ. of Hawaii, Honolulu, HI, 3Macquarie Univ., Sydney, AUSTRALIA.

Integrons are genetic elements, found in ~10% of bacteria, composed of a gene coding for an integrase, which function is to insert and remove small mobile elements called gene cassettes at a nearby integration site. In the human pathogen Vibrio cholerae, integrons can occupy up to 3% of their host genome and contain >170 gene cassettes coding for a variety of functions, including pathogenicity factors, antibiotic resistance determinants and toxins. To determine the role of this hyperecombinogenic genomic hotspot in the evolution of V. cholerae, we sequenced 1337 gene cassettes from 20 isolates belonging to a population from a single brackish pond. Over 250 unique cassette types could be identified, representing a wide range of functions. Although the most abundant cassette types in our dataset could not be assigned a function, examples of both purifying and diversifying selection could be found among them. The gene cassette pool associated with V. cholerae integrons was distinct from those of other vibrios, only showing partial overlap in composition. This gene pool was also large, as no pair of strains shared more than 50% of their cassettes, with little overlap between the genes cassettes found in the integrons of environmental and clinical V. cholerae strains. These results indicate limited flow of gene cassette between integrons of different vibrio species as well as the existence of a diverse gene pool largely segregated from the greater genomic gene pool of marine environments.