Absence of BapA type III effector protein affects Burkholderia pseudomallei intracellular lifecycle in human host cells.

[Display omitted] • bapA gene knockout to study role of type 3 effector BapA in B. pseudomallei intracellular lifecycle. • Mutant showed attenuation in attachment and entry into A549 cells with unaffected intracellular replication. • Mutant demonstrated impaired cell-to-cell spreading with no evident defect in actin tail formation. • Mutant displayed reduced phagocytosis and intracellular replication rates in macrophage cells. • BapA may be important in the early stages of B.pseudomallei intracellular lifecycle. The etiological agent of melioidosis, Burkholderia pseudomallei , utilises a type III secretion system cluster 3 (T3SS3) to deliver proteins termed type III effectors (T3SEs) into the host cytoplasm in order to establish an intracellular lifecycle in phagocytic and non-phagocytic cells, thus playing an important role in pathogenesis. To gain insight into possible functional roles for BapA, a putative T3SE with unknown function, in the intracellular lifecycle of B.pseudomallei , bapA gene knockout mutant was constructed. The effect of the knockout on virulence to the otherwise isogenic parental strain, K96243, was studied by cellular infection assays and Caenorhabditis elegans killing assay. The attachment and subsequent entry into A549 cells was significantly (P < 0.05) attenuated in the Δ bapA compared to K96243. However, intracellular replication was not affected. Furthermore, the cell-to-cell spreading capacity of Δ bapA was impaired although the mutant exhibited no evident defect in its actin tail formation. Additionally, phagocytosis and intracellular replication rates of Δ bapA in U937 macrophage cells were significantly reduced relative to K96243 without phagosomal escape being affected. Based on these observations, we conclude that the BapA T3SE could play an important role in B.pseudomallei intracellular lifecycle, especially, in the early stages of attachment and entry into the host cell. [ABSTRACT FROM AUTHOR]