Grossman Alex S, Lei Lei, Botting Jack M, Liu Jett, Nahar Nusrat, Liu Jun, McLean Jeffrey S, He Xuesong, Bor Batbileg
Department of Microbiology, ADA Forsyth Institute, Somerville, MA 02143, United States.
West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan 610093, China.
ISME J. 2025 Jan 2;19(1). doi: 10.1093/ismejo/wraf119.
All cultivated Patescibacteria, also known as the candidate phyla radiation, are obligate episymbionts residing on other microbes. Despite being ubiquitous in many diverse environments, including mammalian microbiomes, molecular mechanisms of host identification and binding amongst ultrasmall bacterial episymbionts remain largely unknown. Type 4 pili are well conserved in this group and could potentially facilitate these symbiotic interactions. To test this hypothesis, we genetically targeted pili genes in Saccharibacteria Nanosynbacter lyticus strain TM7x to assess their essentiality and roles in symbiosis. Our results revealed that N. lyticus assembles two distinct type 4 pili: a nonessential thin pilus that has the smallest diameter of any type 4 pili and contributes to host-binding and episymbiont growth; and an essential thick pilus involved in twitching motility. To understand the role of these pili in vivo we developed Saccharibacteria competition assays and species-specific Fluorescence in situ hybridization probes. Competition between different Saccharibacteria within mock communities demonstrated consistent competitive outcomes that were not driven by priority effects but were dependent on the thin pilus. Collectively, our findings demonstrate that Saccharibacteria encode unique extracellular pili that enable their underexplored episymbiotic lifestyle and competitive fitness within a community.
所有培养的Patescibacteria，也被称为候选门辐射类群，都是寄生于其他微生物的专性外共生菌。尽管它们在包括哺乳动物微生物群在内的许多不同环境中普遍存在，但超小型细菌外共生菌中宿主识别和结合的分子机制仍 largely unknown。4型菌毛在这一类群中高度保守，可能有助于这些共生相互作用。为了验证这一假设，我们对溶菌性纳米共生菌（Saccharibacteria Nanosynbacter lyticus）菌株TM7x中的菌毛基因进行了基因靶向，以评估它们在共生中的必要性和作用。我们的结果表明溶菌性纳米共生菌组装了两种不同的4型菌毛：一种非必需的细菌毛，其直径是所有4型菌毛中最小的，有助于宿主结合和外共生菌生长；另一种必需的粗菌毛参与了颤动运动。为了了解这些菌毛在体内的作用，我们开发了Saccharibacteria竞争试验和物种特异性荧光原位杂交探针。模拟群落中不同Saccharibacteria之间的竞争显示出一致的竞争结果，这些结果不是由优先效应驱动的，而是依赖于细菌毛。总的来说，我们的研究结果表明，Saccharibacteria编码独特的细胞外菌毛，这使得它们未被充分探索的外共生生活方式和在群落中的竞争适应性成为可能。
