title: Phase-locked mutants of Mycoplasma agalactiae: defining the molecular switch of high-frequency Vpma antigenic variation.
abstract: Mycoplasma agalactiae, an important pathogen of small ruminants, exhibits antigenic diversity by switching the expression of multiple surface lipoproteins called Vpmas (Variable proteins of M. agalactiae). Although phase variation has been shown to play important roles in many host-pathogen interactions, the biological significance and the mechanism of Vpma oscillations remain largely unclear. Here, we demonstrate that all six Vpma proteins are expressed in the type strain PG2 and all undergo phase variation at an unusually high frequency. Furthermore, targeted gene disruption of the xer1 gene encoding a putative site-specific recombinase adjacent to the vpma locus was accomplished via homologous recombination using a replicon-based vector. Inactivation of xer1 abolished further Vpma switching and the 'phase-locked' mutants (PLMs) continued to steadily express only a single Vpma product. Complementation of the wild-type xer1 gene in PLMs restored Vpma phase variation thereby proving that Xer1 is essential for vpma inversions. The study is not only instrumental in enhancing our ability to understand the role of Vpmas in M. agalactiae infections but also provides useful molecular approaches to study potential disease factors in other 'difficult-to-manipulate' mycoplasmas.
authors.affiliation: Institute of Bacteriology, Mycology and Hygiene, Department of Pathobiology, University of Veterinary Medicine Vienna, Veterinärplatz 1, A-1210 Vienna, Austria. Rohini.Chopra-Dewasthaly@vu-wien.ac.at
authors.forename: Rohini
authors.initials: R
authors.lastname: Chopra-Dewasthaly
authors.forename: Christine
authors.initials: C
authors.lastname: Citti
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Glew
authors.forename: Martina
authors.initials: M
authors.lastname: Zimmermann
authors.forename: Renate
authors.initials: R
authors.lastname: Rosengarten
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Jechlinger
mesh_terms: D000940:Antigenic Variation; D001426:Bacterial Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D015153:Blotting, Western; D023061:Gene Order; D005816:Genetic Complementation Test; D009154:Mutation; D045644:Mycoplasma agalactiae / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics; D045522:Recombinases / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic
chemical_list: D001426:Bacterial Proteins; D045522:Recombinases