Vpma variation of Mycoplasma agalactiae and pathogenesis

Compared to other bacterial pathogens, the current knowledge of the molecular basis of pathogenicity of mycoplasmas is limited, and their strategies of infection at the molecular and cellular level remain to be elucidated. Several studies in the past years have shown that pathogenic mycoplasmas are equipped with sophisticated genetic systems, which allow these agents to spontaneously change their surface antigenic make-up. It is implicated that these variable surface components provide the wall-less mycoplasmas with a means to avoid the host immune response and promote host colonization. In Mycoplasma agalactiae, the agent of "contagious agalactia" in sheep and goats, a pathogenicity island-like locus has recently been identified that contains six distinct but related genes which encode the major immunodominant membrane proteins, the so-called Vpmas. It was shown that these surface-associated proteins vary in expression at an unusual high frequency due to DNA rearrangements mediated by the site-specific Xer1 recombinase. The previous lack of tools to genetically manipulate M. agalactiae has hampered more refined studies to assess the exact function of Vpmas in M. agalactiae infection and disease. The development of immunological reagents to monitor Vpma phenotypic variation in vivo during infection and the targeted disruption of the xer1 recombinase gene resulting in Vpma phase-locked mutants represent important breakthroughs which set up the basis to assess the role of Vpmas in molecular pathogenesis. Phase-locked mutants display a stable Vpma phenotype and are steadily expressing a single, well-characterized Vpma product. The present research project is designed to define the significance of Vpma oscillation under in vivo conditions in the natural host using phase-locked mutants in experimental infection studies and to evaluate the mode of action and regulation of the Xer1 recombinase in vitro and in vivo.

Compared to other bacterial pathogens, the current knowledge of the molecular basis of pathogenicity of mycoplasmas is limited, and their strategies of infection at the molecular and cellular level remain to be elucidated. Several studies in the past years have shown that pathogenic mycoplasmas are equipped with sophisticated genetic systems, which allow these agents to spontaneously change their surface antigenic make-up. It is implicated that these variable surface components provide the wall-less mycoplasmas with a means to avoid the host immune response and promote host colonization. In Mycoplasma agalactiae, the agent of "contagious agalactia" in sheep and goats, a pathogenicity island-like locus has recently been identified that contains six distinct but related genes which encode the major immunodominant membrane proteins, the so-called Vpmas. It was shown that these surface-associated proteins vary in expression at an unusual high frequency due to DNA rearrangements mediated by the site-specific Xer1 recombinase. The previous lack of tools to genetically manipulate M. agalactiae has hampered more refined studies to assess the exact function of Vpmas in M. agalactiae infection and disease. The development of immunological reagents to monitor Vpma phenotypic variation in vivo during infection and the targeted disruption of the xer1 recombinase gene resulting in Vpma phase-locked mutants represent important breakthroughs which set up the basis to assess the role of Vpmas in molecular pathogenesis. Phase-locked mutants display a stable Vpma phenotype and are steadily expressing a single, well-characterized Vpma product. The present research project is designed to define the significance of Vpma oscillation under in vivo conditions in the natural host using phase-locked mutants in experimental infection studies and to evaluate the mode of action and regulation of the Xer1 recombinase in vitro and in vivo.