Shewanella species as potential horizontal transfer vectors of S.ma.I2-like group II introns.

QUIROGA C, VAZQUEZ SC, PARMECIANO DI NOTO G, MAC CORMACK WP, CENTRÓN D

Congreso; IX Congreso Argentino de Microbiología General; 2013

Bacterial group II introns are widely distributed ribozymes capable of self-splicing. These elementshave the ability to move to new regions in a genome through an RNA intermediate by aretrotransposition event. Previously, we found that a class C- group II intron S.ma.I2 from the clinical isolate Serratia marcescens shares a common ancestor with group II introns encoded in marine bacteria. Interest in this genus arose from its biotechnological application as biofuel cells andbioremediation, and recently also due to its relevance as an opportunistic pathogen in soft tissuelesions. The aim of this work was to evaluate the occurrence of S.ma.I2-like class C group II introns among Shewanella isolates and to characterize their genomic contexts.We searched for S.ma.I2 homologues in 10 clinical and 5 marine Shewanella spp. isolates by PCRusing specific primers. Three out of 15 isolates harboured a class C group II intron, corresponding to 1 clinical (S. algae) and 2 marine isolates (Shewanella spp. and S. vesiculosa) isolates. Nucleotide sequence analysis showed that these introns were highly identical to S.ma.I2 (> 95%). Comparative analysis of Shewanella genomes using Artemis showed that out of 24 complete projects, 5 harboured at least one class C group II intron in their chromosomes. In addition, class C group II introns were found in the boundaries of different transposases. We looked for these genes in our 3 intron-bearing Shewanella isolates by PCR; however none of these S.ma.I2-like group II introns were associated to them. In order to identify their insertion sites we did inverse PCR using specific primers. Our results showed that they were inserted in the intergenic region of unknown proteins with no clear association to mobile elements. Sequence analysis of the insertion site using the MFOLD software confirms that alike S.ma.I2, our S.ma.I2-like group II introns also insert downstream of DNA secondary structures. Our experimental and in-silico analyses support the hypothesis that the genus Shewanella may act as a vector that promotes the transfer of S.ma.I2-like group II introns from a marine niche to a clinical environment.