Title

Physical mapping of the genome and elucidation of variable proteins of Mycoplasma gallisepticum

Date of Completion

January 1998

Keywords

Biology, Genetics|Biology, Microbiology|Health Sciences, Immunology

Degree

Ph.D.

Abstract

A physical genomic map of Mycoplasma gallisepticum was constructed as a foundation for the genetic analysis of mycoplasma pathogenicity. A variant phenotype of M. gallisepticum was isolated from an in vitro antibody-culture system utilizing metabolism-inhibiting antibodies against the 64 kDa lipoprotein LP64. Data suggests that the interaction of specific immunoglobulins with target epitopes resulted in the selective growth of a subpopulation of organisms able to escape the metabolism-inhibiting effects of the antibodies. Examination of different strains of M. gallisepticum revealed an intraspecies strain variability in the phenotypes isolated from the in vitro antibody-culture system. Analysis of the variant phenotypes identified several integral membrane proteins which undergo variable expression. Amino acid analysis identified these proteins as products of the pMGA1.9 gene. Hybridization and PCR analysis demonstrate that the pMGA1.9 gene exists as a single copy and its size does not vary among strains. Observed molecular masses and amino acid results suggest that the pMGA1.9 gene is expressed as a mature protein, and that this product is post-translationally modified. The findings of this research suggest that M. gallisepticum utilizes phase and antigenic variation as mechanisms for interacting with host antibodies directed at surface molecules. The ability of M. gallisepticum to vary its membrane proteins might play a significant role in pathogenicity by enabling the organism to evade the host immune response. ^