3D5_7.fastqDivergent Roles of hcp Genes in Salmonella Typhimurium T6SS Shape Gut Microbiota Dysbiosis during InfectionT6SS

<em>Salmonella enterica </em>subsp.<em> enterica </em>serovar Typhimurium (<em>S. </em>Typhimurium) is a facultative intracellular pathogen causing significant gastrointestinal infections in humans and animals. The type VI secretion system (T6SS) plays a crucial role in its virulence, facilitating competition with host gut microbiota and promoting infection. While <em>S.</em> Typhimurium possesses a single T6SS, it encodes three <em>hcp</em> genes, which are crucial for its functionality and may exhibit non-redundant roles. In this study, we used 16S rRNA sequencing to analyze gut microbiota in BALB/c mice after infection with wild-type (WT) <em>S.</em> Typhimurium or mutant strains (Δ<em>hcp1</em>, Δ<em>hcp2</em>, Δ<em>hcp3</em>). Our findings revealed that <em>S</em>. Typhimurium infection induced severe gut dysbiosis especially on the second day post-infection. Specifically, the infection led to a notable increase in Firmicutes and activated the energy pathways that promotes the breakdown of short chain fatty acids. Wild type <em>S.</em> Typhimurium infection caused a sharp increase in <em>Escherichia-Shigella</em> levels, indicating inflammation-related dysbiosis, while the Δ<em>hcp</em>1, Δ<em>hcp</em>2, and Δ<em>hcp</em>3 groups showed milder changes, suggesting less disruption to gut microbiota. Deletion of individual <em>hcp</em> genes led to distinct bacterial taxa changes, underscoring the non-redundant functions of each <em>hcp</em>. Despite having only one T6SS, <em>S.</em> Typhimurium achieves precise modulation of its functions through the divergent roles of its Hcp proteins, enabling efficient colonization and persistence in the host gut.  These findings provide insights into the intricate mechanisms of bacterial adaptation and host-pathogen interactions, offering potential avenues for therapeutic interventions targeting T6SS-mediated dysbiosis.

肠炎沙门氏菌肠炎亚种鼠伤寒血清型（*Salmonella enterica* subsp. *enterica* serovar Typhimurium，简称S. Typhimurium）是一类兼性胞内致病菌，可引发人类与动物的重症胃肠道感染。VI型分泌系统（type VI secretion system, T6SS）在其毒力调控中发挥核心作用，能够介导病原菌与宿主肠道菌群的竞争过程并促进感染建立。尽管S. Typhimurium仅携带一套完整的T6SS，但其基因组编码3个*hcp*基因，这些基因不仅是T6SS功能实现的关键，且各自具备非冗余的生物学功能。本研究采用16S rRNA测序（16S rRNA sequencing）技术，分析了BALB/c小鼠感染野生型（wild-type, WT）S. Typhimurium或其Δhcp1、Δhcp2、Δhcp3突变菌株后的肠道菌群特征。研究结果显示，S. Typhimurium感染可诱发严重的肠道菌群失调，该效应在感染后第2天尤为显著。具体而言，感染可导致厚壁菌门（Firmicutes）的丰度显著升高，并激活促进短链脂肪酸（short chain fatty acids）分解的能量代谢通路。野生型S. Typhimurium感染会引发埃希氏菌-志贺氏菌属（*Escherichia-Shigella*）丰度的急剧上升，提示存在炎症相关的菌群失调；而Δhcp1、Δhcp2及Δhcp3突变株感染组的菌群变化幅度显著降低，表明其对宿主肠道菌群的破坏作用更弱。单个*hcp*基因的缺失会引发独特的细菌类群丰度改变，这进一步证实了各*hcp*基因的非冗余功能。尽管仅拥有一套T6SS，S. Typhimurium可通过其Hcp蛋白的差异化功能实现对T6SS功能的精准调控，从而高效完成在宿主肠道内的定植与持续存活。本研究结果为解析细菌适应性进化与宿主-病原体互作的复杂机制提供了新的研究视角，同时也为靶向T6SS介导的菌群失调的治疗干预策略提供了潜在的开发方向。