Burkholderia pseudomalleiBicA protein promotes pathogenicity in macrophages by regulating Invasion, Intracellular Survival, and Virulence

Abstract

Burkholderia pseudomallei (Bpm)is the causative agent of melioidosis disease.Bpmis a facultative intracellular pathogen with a complex lifecycle inside host cells. Pathogenic success depends on a variety of virulence factors with one of the most critical being the type 6 secretion system (T6SS).Bpmuses the T6SS to move into neighboring cells, resulting in multinucleated giant cells (MNGCs) formation, a strategy used to disseminate from cell-to-cell. Our prior study using a dual RNA-seq analysis to dissect T6SS-mediated virulence on intestinal epithelial cells identified BicA as a factor upregulated in a T6SS mutant (1). BicA regulates both type 3 secretion system (T3SS) and T6SSs; however, the extent of its involvement during disease progression is unclear. To fully dissect the role of BicA during systemic infection, we used two macrophage cell lines paired with a pulmonaryin vivochallenge murine model. We found that ΔbicAhas a distinct intracellular replication defect in both immortalized and primary macrophages that begins as early as 1 h post-infection. This intracellular defect is linked with the lack of cell-to-cell dissemination and MNGC formation, as well as a defect on T3SS expression. Thein vitrophenotype translatedin vivoas ΔbicAwas attenuated in a pulmonary model of infection; demonstrating a distinct macrophage activation profile and lack of pathological features present in the wild type. Overall, these results highlight the role of BicA in regulating intracellular virulence and demonstrate that specific regulation of secretion systems has a significant effect on host response andBpmpathogenesis.ImportanceMelioidosis is an understudied tropical disease that still results in ∼50% fatalities from those infected patients. It is caused by the Gram-negative bacillusBurkholderia pseudomallei(Bpm). Bpmis an intracellular pathogen that disseminates from the infected cell to target organs, causing disseminated disease. Regulation of secretion systems involved in entry and cell-to-cell spread is poorly understood. In this work, we characterize the role of BicA as a regulator of secretion systems during infection of macrophagesin vitroandin vivo. Understanding how these virulence factors are controlled will help us determine their influence on the host cells and define the macrophage responses associated with bacterial clearance.