CONJUGAL TRANSFER OF CHROMOSOMAL DNA IN MYCOBACTERIUM-SMEGMATIS

The genus Mycobacterium includes the major human pathogens Mycobacteri um tuberculosis and Mycobacterium leprae. The development of rational drug treatments for the diseases caused by these and other mycobacteri a requires the establishment of basic molecular techniques to determin e the genetic basis of pathogenesis and drug resistance. To date, the ability to manipulate and move DNA between mycobacterial strains has r elied on the processes of transformation and transduction; Here, we de scribe a naturally occurring conjugation system present in Mycobacteri um smegmatis, which we anticipate will further facilitate the ability to manipulate the mycobacterial genome. Our data rule out transduction and transformation as possible mechanisms of gene transfer in this sy stem and are most consistent with conjugal transfer. We show that reco mbinants are not the result of cell fusion and that transfer occurs fr om a distinct donor to a recipient. One of the donor strains is mc(2)1 55, a highly transformable derivative that is considered the prototype laboratory strain for mycobacterial genetics; the demonstration that it is conjugative should increase its genetic manipulability dramatica lly. During conjugation, extensive regions of chromosomal DNA are tran sferred into the recipient and then integrated into the recipient chro mosome by multiple recombination events. We propose that DNA transfer is occurring by a mechanism similar to Hfr conjugation in Escherichia coli.