Bartonella henselaetrimeric autotransporter adhesin BadA expression interferes with effector translocation by the VirB/D4 type IV secretion system

Abstract

SummaryThe Gram-negative, zoonotic pathogen Bartonella henselae is the aetiological agent of cat scratch disease, bacillary angiomatosis and peliosis hepatis in humans. Two pathogenicity factors of B. henselae -each displaying multiple functions in host cell interaction -have been characterized in greater detail: the trimeric autotransporter Bartonella adhesin A (BadA) and the type IV secretion system VirB/D4 (VirB/D4 T4SS). BadA mediates, e.g. binding to fibronectin (Fn), adherence to endothelial cells (ECs) and secretion of vascular endothelial growth factor (VEGF). VirB/D4 translocates several Bartonella effector proteins (Beps) into the cytoplasm of infected ECs, resulting, e.g. in uptake of bacterial aggregates via the invasome structure, inhibition of apoptosis and activation of a proangiogenic phenotype. Despite this knowledge of the individual activities of BadA or VirB/D4 it is unknown whether these major virulence factors affect each other in their specific activities. In this study, expression and function of BadA and VirB/D4 were analysed in a variety of clinical B. henselae isolates. Data revealed that most isolates have lost expression of either BadA or VirB/D4 during in vitro passages. However, the phenotypic effects of coexpression of both virulence factors was studied in one clinical isolate that was found to stably coexpress BadA and VirB/ D4, as well as by ectopic expression of BadA in a strain expressing VirB/D4 but not BadA. BadA, which forms a dense layer on the bacterial surface, negatively affected VirB/D4-dependent Bep translocation and invasome formation by likely preventing close contact between the bacterial cell envelope and the host cell membrane. In contrast, BadA-dependent Fn binding, adhesion to ECs and VEGF secretion were not affected by a functional VirB/D4 T4SS. The obtained data imply that the essential virulence factors BadA and VirB/D4 are likely differentially expressed during different stages of the infection cycle of Bartonella.

Heterologous Expression of Bartonella Adhesin A in Escherichia coli by Exchange of Trimeric Autotransporter Adhesin Domains Results in Enhanced Adhesion Properties and a Pathogenic Phenotype

“…Surprisingly, and in contrast to what occurs in Y. enterocolitica, where YadA enhances type III secretion of Yersinia outer proteins into host cells (34), injection of Bartonella effector proteins (Beps) into host cells by the B. henselae VirB/D4 type 4 secretion system is inhibited by BadA expression (17). However, it has to be emphasized that functional analysis of single BadA domains by orthologous expression in B. henselae is complicated by the limited number of genetic tools for construction of such mutants and the very slow growth of the pathogen (6).…”

“…A crucial role of B. henselae BadA in the infection process of ECs was demonstrated (4), and the head domain of BadA turned out to be decisive for EC binding (15). However, B. henselae harbors further potential adhesins in its genome, e.g., filamentous hemagglutinins (17,28), which might interact with this process. Therefore, we investigated BadA-mediated adherence to ECs using E. coli expressing BadA HN23 hybrid 3.…”

“…Recently, the stalk region was identified to represent the Fn-binding site, and a minimal length of four neck-stalk repeats is crucial for Fn binding (16). Additionally, the function of the B. henselae VirB/D4 type 4 secretion system depends on the expression and length of BadA: the longer the BadA construct, the less efficient was the secretion of effector proteins into host cells (17).…”

Analysis of Endothelial Adherence of Bartonella henselae and Acinetobacter baumannii Using a Dynamic Human Ex Vivo Infection Model

“…TAA-dependent adherence of B. henselae and A. baumannii. Since the role of BadA in mediating bacterial adherence to ECs has been analyzed in detail (2,5,6,32,33), B. henselae was used in our study as a control to calibrate the experiments with A. baumannii. Previous works described mainly Ata-dependent adhesion abilities of A. baumannii to ECMs under static infection conditions (3).…”

Bartonella and Brucella--Weapons and Strategies for Stealth Attack

“…Bartonella TAAs additionally induce angiogenesis and serum resistance (O'Rourke et al 2011). Interestingly, BadA expression on the bacterial surface masks the activity of the VirB T4SS (Lu et al 2013), but these two major virulence factors are differentially regulated on the transcriptional level via the TC system BatS/ BatR, indicating that the two act at different stages of the infection process.…”