Identification of a genomic fragment of Mycobacterium tuberculosis contributing to in vivo growth advantage

Abstract

The work presented here describes the development and testing of novel molecular tools and genetic methods that may be used to identify determinants of virulence of the pathogenic mycobacteria. The methods were used to isolate a genomic fragment of the virulent Mycobacterium tuberculosis strain H37Rv that confers an in vivo growth advantage to the avirulent strain H37Ra.;We developed systems that utilized genetic complementation to isolate genomic fragments of pathogenic mycobacteria that may be associated with virulence. Genomic shuttle cosmid libraries of many mycobacterial species were constructed and characterized. Integrating shuttle cosmid libraries were developed as a tool uniquely suited for in vivo complementation because they replicate as a single copy with the chromosome and do not require antibiotic selection for their stability.;The relative virulence of M. tuberculosis strains H37Ra and H37Rv is correlated with growth rate in mouse spleen and lung. Since H37Rv replicates in mouse spleen and lung, and H37Ra does not, we chose to enrich for individual growing recombinants from a pool of H37Ra transformants harboring the H37Rv library by in vivo selection. A molecular strategy was devised to isolate and clone the H37Rv DNA from in vivo-selected clones. A 25 kb H37Rv genomic fragment, ivg, that conferred in vivo growth advantage to H37Ra was identified.