BPSS1504, a Cluster 1 Type VI Secretion Gene, Is Involved in Intracellular Survival and Virulence of Burkholderia pseudomallei

Abstract

ABSTRACTBurkholderia pseudomalleiis a Gram-negative rod and the causative agent of melioidosis, an emerging infectious disease of tropical and subtropical areas worldwide.B. pseudomalleiharbors a remarkable number of virulence factors, including six type VI secretion systems (T6SS). Using our previously described plaque assay screening system, we identified aB. pseudomalleitransposon mutant defective in theBPSS1504gene that showed reduced plaque formation. TheBPSS1504locus is encoded within T6SS cluster 1 (T6SS1), which is known to be involved in the pathogenesis ofB. pseudomalleiin mammalian hosts. For further analysis, aB. pseudomalleiBPSS1504deletion (BpΔBPSS1504) mutant and complemented mutant strain were constructed.B. pseudomalleilacking theBPSS1504gene was highly attenuated in BALB/c mice, whereas thein vivovirulence of the complemented mutant strain was fully restored to the wild-type level. TheBpΔBPSS1504mutant showed impaired intracellular replication and formation of multinucleated giant cells in macrophages compared with wild-type bacteria, whereas the induction of actin tail formation within host cells was not affected. These observations resembled the phenotype of a mutant lackinghcp1, which is an integral component of the T6SS1 apparatus and is associated with full functionality of the T6SS1. Transcriptional expression of the T6SS componentsvgrG,tssA, andhcp1, as well as the T6SS regulatorsvirAG,bprC, andbsaN, was not dependent onBPSS1504expression. However, secretion of Hcp1 was not detectable in the absence ofBPSS1504. Thus, BPSS1504 seems to serve as a T6SS component that affects Hcp1 secretion and is therefore involved in the integrity of the T6SS1 apparatus.