Elementos de captura génica en ambientes naturalesINTEGRONES

Resumen

The adquisition of elements that contribute to the propagation of antibiotic resistance genes such as plasmids, bacteriophages, integrative conjugative elements, transposons, IS elements or genomic islands by Horizontal Gene Transfer (HGT), increases genetic diversity (de la Cruz and Davies 2000) and contribute, in many cases, to bacterial evolution and adaptability to the environment (Michael et al. 2004). Integrons are gene capture elements that contain the elements necessary for incorporating, by a recombination event mediated by an integrase, foreign DNA (gene cassettes) at specific recombination sites (attI) and their expression through a promoter (Pc) (Mazel 2006). They possess two conserved regions separated by a variable region containing one or more genes integrated as cassettes (Stokes et al. 2001). The best studied integrons are those responsible for antibiotic resistance in human pathogens but antibiotics resistance genes are not only restricted to clinical environments, in fact, the origin of these genes is in environmental microorganisms. We also know that pollution produces changes in the biosphere, including the microbiota, and might modify, due to its selective pressure, the prevalence and activity of elements involved in HGT. In this thesis, we investigate, the presence of integrons in natural nonclinical contaminated ecosystems, uncontaminated, away from human activity and intestinal human samples, using bioinformatics and metagenomic techniques. We found several integron integrases, including type 1 integrases, as well as conserved regions and gene cassettes, distributed in all the environmental samples analyzed, indicating that these elements are widely distributed in natural nonclinical environments. In fact, most sequences obtained are new, which indicates the existence of a variety of integrons in the environment. Despite being new sequences, most of them have common domains with previously described type 1 integrase. The intestinal human samples investigated showed less variability considering that we only found one integron integrase type 1. We have no clear evidence at present to support the conclusion that contamination increases the presence of certain integrases in natural ecosystems. The analysis of genomic and metagenomic databases searching for integrons showed similar results to those obtained when we investigate integrons in clinical and nonclinical environments. Studying the presence of integrons in different environments is important to understand the function of these elements as a reservoir of genes and their contribution in bacterial evolution, adaptability and antibiotic resistance.