Trimeric Autotransporters of Haemophilus parasuis : Generation of an Extensive Passenger Domain Repertoire Specific for Pathogenic Strains

Haemophilus parasuis is the agent responsible for causing Glässer's disease, but little is known about the pathogenic determinants of this major pig disease. Here we describe, for the pathogenic strain Nagasaki, the molecular characterization of 13 trimeric autotransporters as assessed by the presence of YadA C-terminal translocator domains which were classified into three groups. All passenger domains possess motifs and repeats characteristic of adhesins, hemagglutinins, and invasins with various centrally located copies of collagen-like repeats. This domain architecture is shared with two trimeric autotransporter proteins ofH. somnus 129Pt. Genomic comparison by microarray hybridization demonstrated homologies amongH. parasuis virulent strains and high divergence with respect to nonvirulent strains. Therefore, these genes were namedvtaA (v irulence-associatedt rimerica utotransporters). The sequencing of 17 homologousvtaA genes of different invasive strains highlighted an extensive mosaic structure. Based also on the presence of DNA uptake signal sequences within thevtaA genes, we propose a mechanism of evolution by which gene duplication and the accumulation of mutations and recombinations, plus the lateral gene transfer of the passenger domain, led to the diversity of this multigene family. This study provides insights to help understand the tissue colonization and invasiveness characteristic ofH. parasuis pathogenic strains.