The health of mammals depends on a complex interplay with their microbial ecosystems. Compartments exposed to external environments such as the mucosal surfaces of the gastrointestinal tract accommodate the gut microbiota, composed by a wide range of bacteria. The gut microbiome confers benefits to the host, including expansion of metabolic potential and the development of an immune system that can robustly protect from external and internal insults. The cooperation between gut microbiome and host is enabled in part by the formation of partitioned niches that harbor diverse bacterial phyla. Bacterial secretion systems are commonly employed to manipulate the composition of these local environments. Here, we explore the roles of the bacterial type VI secretion system (T6SS), present in ~25% of gram-negative bacteria, including many symbionts, in the establishment and perturbation of bacterial commensalism, and symbiosis in host mucosal sites. This versatile apparatus drives bacterial competition, although in some cases can also interfere directly with host cells and facilitate nutrient acquisition. In addition, some bacterial pathogens cause disease when their T6SS leads to dysbiosis and subverts host immune responses in defined animal models. This review explores our knowledge of the T6SS in the context of the “host-microbiota-pathogen” triumvirate and examines contexts in which the importance of this secretion system may be underappreciated.

哺乳动物的健康取决于与其微生物生态系统的复杂相互作用。暴露于外部环境（例如胃肠道粘膜表面）的隔室可容纳由多种细菌组成的肠道微生物群。肠道微生物组可为宿主带来益处，包括代谢潜能的扩展和免疫系统的发展，可以强有力地保护其免受外部和内部侵害。肠道微生物组与宿主之间的合作在一定程度上是通过形成具有不同细菌门的分区生态位而实现的。细菌分泌系统通常用于操纵这些局部环境的组成。在这里，我们探讨了大约25％的革兰氏阴性细菌（包括许多共生体）中存在的VI型细菌分泌系统（T6SS）的作用，细菌共生主义的建立和摄动，以及宿主黏膜部位的共生。尽管在某些情况下还可以直接干扰宿主细胞并促进营养吸收，但是这种多功能的仪器推动了细菌的竞争。此外，某些细菌病原体的T6SS导致营养不良并破坏特定动物模型中的宿主免疫反应时，会引起疾病。这篇综述探索了我们在“宿主-微生物-病原体”的背景下对T6SS的了解，并探讨了可能未充分认识到该分泌系统重要性的背景。尽管在某些情况下也会直接干扰宿主细胞并促进营养获取。此外，某些细菌病原体的T6SS导致营养不良并破坏特定动物模型中的宿主免疫反应时，会引起疾病。这篇综述探索了我们在“宿主-微生物-病原体”的背景下对T6SS的了解，并探讨了可能未充分认识到该分泌系统重要性的背景。尽管在某些情况下也会直接干扰宿主细胞并促进营养获取。此外，某些细菌病原体的T6SS导致营养不良并破坏特定动物模型中的宿主免疫反应时，会引起疾病。这篇综述探索了我们在“宿主-微生物-病原体”的背景下对T6SS的了解，并探讨了可能未充分认识到该分泌系统重要性的背景。