ABSTRACT

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. Salmonella typhimurium is an important foodborne pathogen. There are three copies of hcp genes identified in S. Typhimurium 14028s. This study aimed to characterize the functions of the three Hcp family proteins and to elucidate the interactions among them. The hcp gene deletion mutants were constructed by λ Red-based recombination system. Effects of hcp mutation on the pathogenicity of 14028s were studied by bacterial competition assays, Dictyostelium discoideum assays and mouse model. The three Hcp family proteins were found to play different roles. Hcp1 can affect the transcription of rpoS and type 2 flagellar gene and influence the motility of 14028s. It is also involved in the intracellular survival of 14028s in Dictyostelium discoideum; 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 hcp gene can result in a transcription level variation in the other two hcp genes. Our findings elucidated the functions of the three Hcp family proteins in S.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.

摘要

VI型分泌系统（T6SS）是一种新的分泌系统，广泛分布于革兰氏阴性细菌中。核心成分溶血素核心调节蛋白（Hcp）既可以用作其结构蛋白又可以用作分泌蛋白或伴侣蛋白。对Hcp的研究对于阐明T6SS的整体毒力机制非常重要。鼠伤寒沙门氏菌是重要的食源性病原体。在S中鉴定出hcp基因的三个副本。鼠伤寒14028s。这项研究旨在表征三种Hcp家族蛋白的功能，并阐明它们之间的相互作用。的HCP基因缺失突变体通过λ基于RED的重组系统构成。的影响HCP通过细菌竞争实验，盘基网柄菌和小鼠模型研究了14028s致病性突变。发现三种Hcp家族蛋白起不同的作用。Hcp1可以影响rpoS和2型鞭毛基因的转录并影响14028s的运动。它也参与14028s的细胞内生存粘菌; Hcp2参与小鼠14028s的早期增殖能力，可防止其过度增殖。Hcp3在这些测定中未显示直接功能。Hcp1可以与Hcp2和Hcp3交互。删除一个hcp基因可能导致其他两个hcp的转录水平发生变化基因。我们的研究结果阐明在三种HCP家族蛋白的功能小号.Typhimurium和说明，有不同的HCP蛋白质之间的相互作用。这项研究将有助于全面了解T6SS在生物体内的作用。