N-176. Environmental Assessment of Integron Gene Cassettes Present in a Tar Pond

J. E. Koenig1, C. Sharp1, Y. Boucher2, W. F. Doolittle1;
1Dalhousie Univ., Halifax, NS, CANADA, 2Massachusetts Inst. of Technology, Cambridge, MA.

Background: The integron is a genetic platform in bacteria that promotes Lateral Gene Transfer (LGT) by performing integron-integrase site-specific recombination of gene cassettes. Research has shown that integron gene cassettes encode an abundance of antibiotic-resistance proteins in clinical pathogens suggesting that the integron plays a significant role in bacterial adaptation to antimicrobials. Given this specific example, we wanted to test whether or not different cassettes might be recruited by the integron according to alternative selection regimes. Methods: Specifically, we examined integron gene cassette content by amplifying, cloning, sequencing, and functionally identifying cassettes from six spatially separated soil samples collected from an industrial site in Sydney, Cape Breton, Nova Scotia, Canada. This site is known to contain high levels of contaminants associated with steel production mainly, the by-products of partial coal combustion. Results: A total of 2,748 integron gene cassettes were recovered from the six different soil sample sites. Among these are cassettes that encode enzymes involved in the degradation of aromatic hydrocarbons including carbazole, a heterocyclic aromatic compound produced during coal gasification. In addition to this, BLAST similarity searches of gene cassette-encoded proteins show that the majority of cassettes with homologs in the NCBI database are most similar to proteins present in the Pseudomonas, a genus well known for its ability to degrade xenobiotics. Furthermore, we observe that the two most contaminated soil samples of those considered share the most integron gene cassette-encoded functional overlap. Conclusion: The integron gene cassette-encoded function, cassette taxonomic distribution, and cassette similarity profiles between the more polluted soil samples support the hypothesis that evolution of integron gene cassette-encoded function may be influenced by environmental parameters. Specifically, we observe that the integron encodes determinants that are likely involved in the degradation of contaminants present in their tar pond environment.