Abstract
Brucella spp. remodel host cellular membrane transport pathways via delivery of Type IV secretion (T4SS) effector proteins to generate a replication-permissive vacuole (rBCV) that supports their intracellular proliferation. Whether Type IV effectors also mediates intracellular growth within the replication vacuole is mostly unknown. Here we show that the T4SS effector BspF is not required for rBCV biogenesis but specifically promotes Brucella replication within rBCVs. Ectopically expressed and bacterially delivered BspF interfered with vesicular transport between the trans-Golgi network (TGN) and recycling endocytic compartment. BspF targeted the recycling endosome, inhibited retrograde traffic to the TGN and interacted with the Arf6 GTPase-activating Protein (GAP) ACAP1 to dysregulate Arf6-/Rab8a-dependent transport within the recycling endosome, which resulted in accretion of TGN-associated vesicles by rBCVs and enhanced bacterial growth. The predicted structure of BspF and interaction with ACAP1 identified residues within its Gcn5-related acetyltransferase (GNAT) domain required for BspF’s modulation of Arf6 activity through ACAP1, the resulting interference with retrograde transport and BspF’s role in bacterial intracellular growth. Altogether, these findings provide mechanistic insight into Brucella modulation of membrane transport that promotes their own proliferation within intracellular vacuoles
