Characterization of BcaA, a Putative Classical Autotransporter Protein in Burkholderia pseudomallei

Abstract

bBurkholderia pseudomallei is a tier 1 select agent, and the causative agent of melioidosis, a disease with effects ranging from chronic abscesses to fulminant pneumonia and septic shock, which can be rapidly fatal. Autotransporters (ATs) are outer membrane proteins belonging to the type V secretion system family, and many have been shown to play crucial roles in pathogenesis. The open reading frame Bp1026b_II1054 (bcaA) in B. pseudomallei strain 1026b is predicted to encode a classical autotransporter protein with an approximately 80-kDa passenger domain that contains a subtilisin-related domain. Immediately 3= to bcaA is Bp11026_II1055 (bcaB), which encodes a putative prolyl 4-hydroxylase. To investigate the role of these genes in pathogenesis, large in-frame deletion mutations of bcaA and bcaB were constructed in strain Bp340, an efflux pump mutant derivative of the melioidosis clinical isolate 1026b. Comparison of Bp340⌬bcaA and Bp340⌬bcaB mutants to wild-type B. pseudomallei in vitro demonstrated similar levels of adherence to A549 lung epithelial cells, but the mutant strains were defective in their ability to invade these cells and to form plaques. In a BALB/c mouse model of intranasal infection, similar bacterial burdens were observed after 48 h in the lungs and liver of mice infected with Bp340⌬bcaA, Bp340⌬bcaB, and wild-type bacteria. However, significantly fewer bacteria were recovered from the spleen of Bp340⌬bcaA-infected mice, supporting the idea of a role for this AT in dissemination or in survival in the passage from the site of infection to the spleen.

Type V Secretion Systems in Bacteria

“…In the case of BcaA, plasmid complementation showed that it is required for efficient plaque formation. In vivo studies indicated that BcaA is also required for efficient dissemination and survival of bacteria in spleen (118). In a less targeted approach, transposon mutagenesis with TnphoA was used to identify potential genes encoding surface-exposed virulence factors in enterotoxigenic E. coli.…”

Recent Advances in Burkholderia mallei and B. pseudomallei Research

“…Another study by Campos et al demonstrated that B. pseudomallei strain 340 bcaA and bcaB mutants displayed impaired invasion and decreased plaque formation in lung epithelial cells [13]. Furthermore, a BALB/c i.n.…”

Antibodies against In Vivo -Expressed Antigens Are Sufficient To Protect against Lethal Aerosol Infection with Burkholderia mallei and Burkholderia pseudomallei

“…Previous studies have examined the biological roles of all 8 ATs in B. pseudomallei (88)(89)(90). However, only the oligomeric ATs BimA (intracellular motility protein) (91), BoaA (92) and BpaC (93) (host cell adhesion proteins), and BpaB (biofilm and virulence factor) (77) have been functionally characterized in B. mallei.…”