Department of Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hillgrid.10698.36, Chapel Hill, North Carolina, USA.
Department of Microbiology, Oregon State University, Corvallis, Oregon, USA.
mBio. 2022 Apr 26;13(2):e0308521. doi: 10.1128/mbio.03085-21. Epub 2022 Apr 11.
Interbacterial competition is prevalent in host-associated microbiota, where it can shape community structure and function, impacting host health in both positive and negative ways. However, the factors that permit bacteria to discriminate among their various neighbors for targeted elimination of competitors remain elusive. We identified a putative lipoprotein (TasL) in species that mediates cell-cell attachment with a subset of target strains, allowing inhibitors to target specific competitors for elimination. Here, we describe this putative lipoprotein, which is associated with the broadly distributed type VI secretion system (T6SS), by studying symbiotic Vibrio fischeri, which uses the T6SS to compete for colonization sites in their squid host. We demonstrate that TasL allows V. fischeri cells to restrict T6SS-dependent killing to certain genotypes by selectively integrating competitor cells into aggregates while excluding other cell types. TasL is also required for T6SS-dependent competition within juvenile squid, indicating that the adhesion factor is active in the host. Because TasL homologs are found in other host-associated bacterial species, this newly described cell-cell attachment mechanism has the potential to impact microbiome structure within diverse hosts. T6SSs are broadly distributed interbacterial weapons that share an evolutionary history with bacteriophage. Because the T6SS can be used to kill neighboring cells, it can impact the spatial distribution and biological function of both free-living and host-associated microbial communities. Like their phage relatives, T6SS cells must sufficiently bind competitor cells to deliver their toxic effector proteins through the syringe-like apparatus. Although phage use receptor-binding proteins (RBPs) and tail fibers to selectively bind prey cells, the biophysical properties that mediate this cell-cell contact for T6SS-mediated killing remain unknown. Here, we identified a large, predicted lipoprotein that is coordinately expressed with T6SS proteins and facilitates the contact that is necessary for the T6SS-dependent elimination of competitors in a natural host. Similar to phage RBPs and tail fibers, this lipoprotein is required for T6SS cells to discriminate between prey and nonprey cell types, revealing new insight into prey selection during T6SS-mediated competition.
种间竞争在宿主相关微生物群中普遍存在，它可以影响群落结构和功能，对宿主健康产生积极和消极的影响。然而，允许细菌识别其各种邻居以有针对性地消除竞争者的因素仍然难以捉摸。我们在物种中发现了一种假定的脂蛋白（TasL），它与广泛分布的 VI 型分泌系统（T6SS）相关，介导细胞-细胞附着与目标菌株的子集，允许抑制剂针对特定的竞争者进行消除。在这里，我们通过研究共生的 Fischeri 弧菌来描述这种假定的脂蛋白，该弧菌使用 T6SS 来争夺其鱿鱼宿主中的定植位点。我们证明，TasL 允许 Fischeri 弧菌细胞通过选择性地将竞争细胞整合到聚集体中，同时排除其他细胞类型，从而将 T6SS 依赖性杀伤限制在某些基因型上。TasL 也需要在幼年鱿鱼中进行 T6SS 依赖性竞争，这表明粘附因子在宿主中是活跃的。由于 TasL 同源物存在于其他宿主相关细菌物种中，这种新描述的细胞-细胞附着机制有可能影响不同宿主内微生物组的结构。T6SS 是广泛分布的种间武器，与噬菌体有着共同的进化历史。由于 T6SS 可用于杀死邻近细胞，因此它会影响自由生活和宿主相关微生物群落的空间分布和生物学功能。像它们的噬菌体亲属一样，T6SS 细胞必须足够地结合竞争细胞，以便通过注射器状装置输送其毒性效应蛋白。尽管噬菌体使用受体结合蛋白（RBPs）和尾部纤维来选择性地结合猎物细胞，但介导这种细胞-细胞接触以进行 T6SS 介导的杀伤的生物物理特性仍然未知。在这里，我们鉴定了一种大的、预测的脂蛋白，该脂蛋白与 T6SS 蛋白协调表达，并促进了 T6SS 依赖性消除竞争在天然宿主中的必要接触。与噬菌体 RBPs 和尾部纤维类似，这种脂蛋白对于 T6SS 细胞区分猎物和非猎物细胞类型是必需的，这为 T6SS 介导的竞争中猎物选择提供了新的见解。
