The gene cassette metagenome is a basic resource for bacterial genome evolution

摘要

Lateral gene transfer has been proposed as a fundamental process underlying bacterial diversity. Transposons, plasmids and phage are widespread and have been shown to significantly contribute to lateral gene transfer. However, the processes by which disparate genes are assembled and integrated into the host regulatory network to yield new phenotypes are poorly known. Recent discoveries about the integron/gene cassette system indicate it has the potential to play a role in this process. Gene cassette are small mobile elements typically consisting of a promoter-less of and a recombination site, Integrons are capable of acquisition and re-arrangement of gene cassette and of the expression of their associated genes. The potential of the integron/gene cassette system is thus largely determined by the diversity contained within the cassette pool and the rate at which integrons sample this pool and the rate at which integrons sample this pool. We show here using a polymerase chain reaction (PCR) approach by which the environmental gene cassette (EGC) metagenome can be directly sampled that this metagenome contains both protein-coding and nonprotein coding genes. Environmental gene cassette-associated recombination sites showed greater diversity than previously seen in integron arrays. Class 1 integrons were shown to be capable of accessing this gene pool through test of recombination activity with a representative range of EGCs. We propose that gene cassette represent a vast, repackage genetic resource that could be thought of as a metagenomic template for bacterial evolution.