Distributive Conjugal Transfer: a New Paradigm and Benchmark for Bacterial Horizontal Gene Transfer

Health Research Incorporated/New York State Department Of Health, Menands NY

Investigators

Abstract

The transfer of DNA from one bacterium to another accelerates the evolution of new strains and species. On the negative side, DNA transfer could facilitate the spread of antibiotic resistance genes, complicating infectious disease treatment strategies. On the positive side, DNA transfer could also create bacterial strains with improved beneficial properties, such as the remediation of petroleum-contaminated soil. Mycobacteria are a branch of the bacterial kingdom that includes both pathogens and brownfield soil-dwelling species. A novel kind of highly effective DNA transfer process, in which two cells appear to swap DNA fragments along the whole chromosome, has been described for a common laboratory mycobacterial species. The current project will identify the genes involved in that process, also testing whether distantly related mycobacteria can partake in such a transfer. The project will provide opportunities for undergraduate students and local high school teachers to gain experience in research. Conjugal DNA transfer has been described in Mycobacterium smegmatis, generating transconjugant genomes that are mixtures of the parental strains. Distributive Conjugal Transfer (DCT) differs from traditional plasmid-based conjugation systems both in creating mosaic genomes and in mechanism, and proteins usually found in plasmid transfer systems are absent from mycobacteria. A mating identity locus (mid), which determines donor or recipient activity, has been mapped to a six-gene cluster embedded within a 25-gene locus that encodes the ESX-1 secretion apparatus. The six genes comprising mid will be analyzed for their contribution to establishing mating identity, their functional association with ESX-1 secretion, and their impact on transcriptional pathways that respond to co-culture with a mating partner. DCT will also be tested in other isolates of M. smegmatis, and in other mycobacterial species. Genome sequencing of new isolates will provide comparative data for identifying the mosaicism that is a hallmark of DCT, and provide reference sequences for transconjugants generated in the laboratory. Successful implementation of this objective will provide a broader view of the impact of DCT on gene flow in the Mycobacterium genus, and provide additional genotype/phenotype information for the critical genes of the mid locus.