Burkholderia pseudomallei
BopE suppresses the Rab32-dependent defense pathway to promote its intracellular replication and virulence
Authors: Rao Chenglong , Zhang Ziyuan , Qiao Jianpeng , Nan Dongqi , Wu Pan , Wang Liting , Yao Changhao , Zheng Senquan , Huang Jinzhu , Liao Yaling , Liu Wenzheng , Hu Zhiqiang , Wang Shiwei , Wen Yuan , Yan Jingmin , Mao Xuhu , Li Qian 
Published: October 2024

Melioidosis is a serious infectious disease caused by the Gram-negative bacterium
Burkholderia pseudomallei
. Recently, Rab32-dependent immune vesicles emerge as a critical defense pathway to restrict the intracellular
B. pseudomallei
. However,
B. pseudomallei
can evade host immune vesicles and survive in the cytoplasm, although this mechanism is not well understood. In this study, we found Rab32-dependent vesicles could effectively combat
B. pseudomallei
infection, but not all intracellular
B. pseudomallei
were encapsulated in Rab32-positive vesicles. To explore how
B. pseudomallei
counteracted the Rab32-dependent defense pathway, transcriptomic profiling of
B. pseudomallei
was performed to characterize the response dynamics during infection. We found that the type III secretion system of
B. pseudomallei
was activated, and a variety of effector proteins were highly upregulated. Among them, BopE, BprD, and BipC were shown to interact with Rab32. Interestingly, BopE directly interacts with host Rab32, potentially suppressing Rab32 function by interfering with nucleotide exchange, which in turn restricts the recruitment of Rab32 to bacterial-containing vesicles. Knocking out of BopE can increase the proportion of Rab32-positive vesicles, suppressing the intracellular replication and virulence of
B. pseudomallei
. Collectively, our findings have demonstrated that BopE may be an important effector for
B. pseudomallei
to evade from the Rab32-dependent killing vesicles into the cytosol for survival and replication. Therefore, a deeper understanding of the interaction between BopE and the host Rab32-dependent restriction pathway may provide an effective therapeutic strategy for the elimination of intracellular
B. pseudomallei
.

IMPORTANCE

B. pseudomallei
is facultative intracellular bacterium that has evolved numerous strategies to evade host immune vesicles and survive in the cytoplasm. Rab32-dependent vesicles are one of these immune vesicles, but the mechanism by which
B. pseudomallei
escape Rab32-dependent vesicles remains elusive. Here, we find
B. pseudomallei
infection leading the activation of the type III secretion system (T3SS-3) and increasing the expression of various effectors. Specifically, we identify that BopE, an effector secreted by T3SS-3, triggers vesicle escape to promote
B. pseudomallei
pathogenicity and survival. Mechanistically, BopE suppresses the activation of Rab32 by interfering with nucleotide exchange, ultimately triggering vesicle escape and intracellular survival. We also find knocking out the
bopE
gene can increase the proportion of Rab32-positive vesicles that trap
B. pseudomallei
, dampening the survival of
B. pseudomallei
both
in vitro
and
in vivo
. Taken together, our findings provide insights into the molecular mechanisms of pathogen effector-induced vesicle escape, indicating a potential melioidosis treatment via blocking
B. pseudomallei
BopE-host Rab32 interaction.