Naturally occurring horizontal gene transfer and homologous recombination in Mycobacterium

Abstract

Acquisition of genetic information through horizontal gene transfer (HGT) is an important evolutionary process by which micro-organisms gain novel phenotypic characteristics. In pathogenic bacteria, for example, it facilitates maintenance and enhancement of virulence and spread of drug resistance. In the genus Mycobacterium, to which several primary human pathogens belong, HGT has not been clearly demonstrated. The few existing reports suggesting this process are based on circumstantial evidence of similarity of sequences found in distantly related species. Here, direct evidence of HGT between strains of Mycobacterium avium representing two different serotypes is presented. Conflicting evolutionary histories of genes encoding elements of the glycopeptidolipid (GPL) biosynthesis pathway led to an analysis of the GPL cluster genomic sequences from four Mycobacterium avium strains. The sequence of M. avium strain 2151 appeared to be a mosaic consisting of three regions having alternating identities to either M. avium strains 724 or 104. Maximum-likelihood estimation of two breakpoints allowed a~4100 bp region horizontally transferred into the strain 2151 genome to be pinpointed with confidence. The maintenance of sequence continuity at both breakpoints and the lack of insertional elements at these sites strongly suggest that the integration of foreign DNA occurred by homologous recombination. To our knowledge, this is the first report to demonstrate naturally occurring homologous recombination in Mycobacterium. This previously undiscovered mechanism of genetic exchange may have major implications for the understanding of Mycobacterium pathogenesis.

Mycobacterium avium subsp. paratuberculosis and M. avium subsp. avium Are Independently Evolved Pathogenic Clones of a Much Broader Group of M. avium Organisms

“…S1 and S2 in the supplemental material). These findings concur with evidence of recombination as demonstrated on a small scale by the sequencing of genes of the glycopeptidolipid cluster in four M. avium strains (14). Though novel, these results are perhaps not surprising given the diverse environmental habitats in which M. avium subsp.…”

Frequent Homologous Recombination Events in Mycobacterium tuberculosis PE/PPE Multigene Families: Potential Role in Antigenic Variability

“…Although it has been demonstrated clearly in vitro that slowgrowing mycobacteria are not refractory to homologous recombination (2, 3, 5, 7), the occurrence of such events under natural conditions for the Mycobacterium genus as a whole has rarely been documented (30,31). We previously provided evidence for a naturally occurring homologous recombination event, namely, gene conversion, involving a PE_PGRS duplicated gene pair (28).…”

Comparative analysis and insights into the evolution of gene clusters for glycopeptide antibiotic biosynthesis

“…The evolution of gene clusters has received more attention in the cyanobacteria (Christiansen et al 2003;Moffitt and Neilan 2004;Rantala et al 2004) and in other bacteria (Lopez 2003;Krzywinska et al 2004;Piel et al 2004). On the basis of coherent phylogenetic trees based on 16S rRNA and on portions of the microcystin clusters, Rantala et al (2004) have proposed an ancient origin for the microcystin pathway and speculated that the corresponding gene cluster has been occasionally lost during the evolution of cyanobacterial lineages.…”