Roles of the Hcp family proteins in the pathogenicity of 14028s.

The type VI secretion system (T6SS) is a new secretion system that is widely distributed among Gram-negative bacteria. The core component hemolysin-coregulated protein (Hcp) can be used as both its structural protein and secretory protein or chaperone protein. Studies on Hcp are important to elucidate the overall virulence mechanism of T6SS. is an important foodborne pathogen. There are three copies of genes identified in . Typhimurium 14028s. This study aimed to characterize the functions of the three Hcp family proteins and to elucidate the interactions among them. The gene deletion mutants were constructed by λ Red-based recombination system. Effects of mutation on the pathogenicity of 14028s were studied by bacterial competition assays, assays and mouse model. The three Hcp family proteins were found to play different roles. Hcp1 can affect the transcription of and type 2 flagellar gene and influence the motility of 14028s. It is also involved in the intracellular survival of 14028s in ; Hcp2 is involved in the early proliferative capacity of 14028s in mice and can prevent its excessive proliferation; Hcp3 did not show direct functions in these assays. Hcp1 can interact with Hcp2 and Hcp3. Deletion of one gene can result in a transcription level variation in the other two genes. Our findings elucidated the functions of the three Hcp family proteins in .Typhimurium and illustrated that there are interactions between different Hcp proteins. This study will be helpful to fully understand how T6SS actions in an organism.