A variety of cell surface structures dictate interactions between bacteria and their environment, including their viruses (bacteriophages). Members of the human gut Bacteroidetes characteristically produce several phase-variable capsular polysaccharides (CPSs), but their contributions to bacteriophage interactions are unknown. To begin to understand how CPSs have an impact on Bacteroides–phage interactions, we isolated 71 Bacteroides thetaiotaomicron-infecting bacteriophages from two locations in the United States. Using B. thetaiotaomicron strains that express defined subsets of CPSs, we show that CPSs dictate host tropism for these phages and that expression of non-permissive CPS variants is selected under phage predation, enabling survival. In the absence of CPSs, B. thetaiotaomicron escapes bacteriophage predation by altering expression of eight distinct phase-variable lipoproteins. When constitutively expressed, one of these lipoproteins promotes resistance to multiple bacteriophages. Our results reveal important roles for Bacteroides CPSs and other cell surface structures that allow these bacteria to persist under bacteriophage predation, and hold important implications for using bacteriophages therapeutically to target gut symbionts.

各种细胞表面结构决定了细菌与其环境（包括病毒（噬菌体））之间的相互作用。人类肠道拟杆菌门的成员特征性地产生几种相变荚膜多糖（CPS），但它们对噬菌体相互作用的贡献尚不清楚。为了开始了解 CPS 如何影响拟杆菌-噬菌体相互作用，我们从美国的两个地点分离了 71 个多形拟杆菌感染噬菌体。使用表达特定 CPS 子集的B. thetaiotaomicron菌株，我们表明 CPS 决定这些噬菌体的宿主向性，并且在噬菌体捕食下选择非许可 CPS 变体的表达，从而实现生存。在缺乏 CPS 的情况下，B. thetaiotaomicron通过改变八种不同的相变脂蛋白的表达来逃避噬菌体捕食。当组成型表达时，这些脂蛋白之一会促进对多种噬菌体的抵抗力。我们的结果揭示了拟杆菌CPS 和其他细胞表面结构的重要作用，使这些细菌能够在噬菌体捕食下持续存在，并对使用噬菌体治疗靶向肠道共生体具有重要意义。