First report on the kinetic characterization of a metagenome-derived metallo-beta-lactamase.

RODRIGUEZ MARGARITA; GHIGLIONE BÁRBARA; MOE L; DI CONZA JOSÉ; WOLMAN F; BLATEZKY ESTEBAN; HANDELSMAN J; GUTKIND GABRIEL; POWER PABLO

Congreso; FEMS 2013 - 5th Congress of European Microbiologists; 2013

Beta-Lactamases represent the most relevant mechanism by which bacterial isolates become resistant to most antibiotics, being some of the major groups considered as pandemic worldwide. It is well known that some prevalent beta-lactamase-encoding genes were recruited from the chromosome of environmental species, being disseminated to pathogens, and became a major clinical problem. Metagenomics includes methodologies aimed at the direct recovery of genes or proteins from uncultured microorganisms, generally involving the construction of metagenomic libraries in Escherichia coli, and avoiding the use of culturing techniques. One of the most convenient screening methods is based on the use of selective media for allowing the growth of those clones producing a specific enzyme or protein (activity-driven metagenomics). By this means, metagenomics has been successfully used for screening antimicrobial resistance genes from environmental soil samples, including beta-lactamase-encoding genes, suggesting that the environmental reservoir of resistance genes (known as resistome) could harbor unexplored genes that are prone to be disseminated among pathogens if they are recruited. Antimicrobial resistance genes for different families of antibiotics from environmental soil samples have been disclosed. Among them, several beta-lactamase-encoding genes from the four Ambler classes have been recovered from Alaskan soil samples, being most of them metallo-beta-lactamases (MBLs). We performed the biochemical characterization of a metagenomic-derived beta-lactamase from an Alaskan soil sample, named LRA-12, and analyzed the genetic background for searching putative mobilization signals. These results support the hypothesis of the origin of many beta-lactamases, residing in the chromosome of the environmental resistome with native wide-range activity spectrum towards most beta-lactams, even before being recruited and disseminated among human pathogens. Conservation of the DNA surrounding the bla gene and the lack of putative recombination/transposition signals is in agreement with the origin of the sample, which comes from an antibiotic-free area and therefore the possibility of occurrence of gene exchanges is low.