Functional Characterization of Burkholderia pseudomallei Trimeric

Burkholderia pseudomallei is a tier 1 select agent and the causative agent of melioidosis, a severe and often fatal disease with symptoms ranging from acute pneumonia and septic shock to a chronic infection characterized by abscess formation in the lungs, liver, and spleen. Autotransporters (ATs) are exoproteins belonging to the type V secretion system family, with many playing roles in pathogenesis. The genome of B. pseudomallei strain 1026b encodes nine putative trimeric AT proteins, of which only four have been described. Using a bioinformatic approach, we annotated putative domains within each trimeric AT protein, excluding the well-studied BimA protein, and found short repeated sequences unique to Burkholderia species, as well as an unex-pectedly large proportion of ATs with extended signal peptide regions (ESPRs). To characterize the role of trimeric ATs in patho-genesis, we constructed disruption or deletion mutations in each of eight AT-encoding genes and evaluated the resulting strains for adherence to, invasion of, and plaque formation in A549 cells. The majority of the ATs (and/or the proteins encoded down-stream) contributed to adherence to and efficient invasion of A549 cells. Using a BALB/c mouse model of infection, we deter-mined the contributions of each AT to bacterial burdens in the lungs, liver, and spleen. At 48 h postinoculation, only one strain, Bp340::pDbpaC, demonstrated a defect in dissemination and/or survival in the liver, indicating that BpaC is required for wild-type virulence in this model. Burkholderia pseudomallei is a Gram-negative soil saprotrophand the causative agent of melioidosis, a severe and often sys-temic infection that can occur in both chronic and acute forms (1