Rough morphological variants of Mycobacterium avium. Characterization of genomic deletions resulting in the loss of glycopeptidolipid expression.

Previously, a gene cluster, termed ser2, which encodes for the synthesis of the specific oligosaccharide of the glycopeptidolipid antigen of Mycobacterium avium serovar 2 strain TMC 724, was defined. DNA probes from this cloned ser2 gene cluster have now been used to clone and characterize the ser2 region from a strain of M. avium which produces rough and smooth colony forms and to identify the genetic differences between these morphotypes. Interstrain differences were seen to exist between the ser2 gene cluster of M. avium strains TMC 724 and 2151. In addition, two distinct rough (Rg) genotypes of strain 2151 were defined by this analysis. The first of these, present in the M. avium Rg-0 and Rg-1 variants, was attributed to a deletion of approximately 28 kilobases from smooth variants, including the entire ser2 gene cluster. This particular deletion is thought to be mediated by recombination between repetitive sequences that flank both sides of the 28-kilobase excised region. The second genotype, seen in M. avium Rg-3 and Rg-4 variants, results from the deletion of an undefined amount of DNA from the right of the ser2 gene cluster. Reported separately (Belisle, J. T., McNeil, M. R., Chaterjee, D., Inamine, J. M., and Brennan, P. J. (1993) J. Biol. Chem. 268, 10510-10516) are the results of biochemical analyses of the glycopeptidolipid/lipopeptide population of the Rg genotypes which revealed that Rg-0 and Rg-1 possess lipopeptides devoid of all of the sugars of the glycopeptidolipids and are obviously biosynthetic precursors of the glycopeptidolipids. These studies help formulate a definition of the physiological effects of glycolipid expression, the biosynthetic and genetic mechanisms involved in their formation, and toward an understanding of the role of M. avium as a serious opportunistic pathogen.