Host-Like Conditions Are Required for T6SS-Mediated Competition among Vibrio fischeri Light Organ Symbionts.
Host-Like Conditions Are Required for T6SS-Mediated Competition among Vibrio fischeri Light Organ Symbionts.
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DOI：
10.1128/msphere.01288-20
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发表时间：
2021-08-25
期刊：
影响因子：
4.8
通讯作者：
Septer AN
中科院分区：
文献类型：
--
作者：
Speare L;Woo M;Bultman KM;Mandel MJ;Wollenberg MS;Septer AN
细菌采用不同的竞争策略来增强适应性并促进自身繁殖。然而，很少有人知道共生细菌如何调节竞争机制，因为它们竞争的主机利基。细菌费氏弧菌与海洋动物形成共生关系，并编码VI型分泌系统（T6 SS），这是一种接触依赖性的杀伤机制，用于在Euprymna spleopes鱿鱼光器官定殖期间消除竞争对手。与其他水平获得的共生体一样，费氏弧菌在共生建立过程中经历了物理和化学环境的变化。因此，我们探讨了环境和主机样条件，以确定生态相关的线索，控制T6 SS依赖的竞争在栖息地过渡。虽然T6 SS在非渗透性条件下没有赋予费氏弧菌菌株ES 401竞争优势，但T6 SS竞争需要宿主样pH和粘度的组合。对于ES 401，高粘度激活T6 SS表达，中性/酸性pH促进细胞-细胞接触以杀死，并且这种pH依赖性表型在所检查的大多数T6 SS编码菌株中是保守的。我们还确定了一个子集的费氏弧菌分离株，从事T6 SS介导的竞争，在高粘度下，在嗜酸性和宿主样pH条件。T6 SS系统发生表明，具有pH依赖性表型的菌株聚集在一起，在pH不依赖性菌株内形成一个亚支，这表明费氏弧菌可能最近进化到限制对宿主生态位的竞争。细菌进化出多种策略来争夺有限的空间和资源。由于这些机制的使用成本可能很高，它们的表达和功能往往局限于利大于弊的特定环境。然而，很少有人知道的具体线索，调节竞争机制的细菌共生体之间的自由生活和宿主栖息地的过渡。在这里，我们使用的生物发光的鱿鱼和鱼共生弧菌fischeri探测主机和环境条件，通过VI型分泌系统控制细菌间的竞争。我们的研究结果确定了一个新的宿主特异性线索，促进许多但不是所有的V. fischeri分离株之间的竞争，强调了研究多个菌株的实用性，以揭示竞争机制如何在密切相关的人群中进行差异调节，因为它们进化以填补不同的小生境。
Bacteria employ diverse competitive strategies to enhance fitness and promote their own propagation. However, little is known about how symbiotic bacteria modulate competitive mechanisms as they compete for a host niche. The bacterium Vibrio fischeri forms a symbiotic relationship with marine animals and encodes a type VI secretion system (T6SS), which is a contact-dependent killing mechanism used to eliminate competitors during colonization of the Euprymna scolopes squid light organ. Like other horizontally acquired symbionts, V. fischeri experiences changes in its physical and chemical environment during symbiosis establishment. Therefore, we probed both environmental and host-like conditions to identify ecologically relevant cues that control T6SS-dependent competition during habitat transition. Although the T6SS did not confer a competitive advantage for V. fischeri strain ES401 under planktonic conditions, a combination of both host-like pH and viscosity was necessary for T6SS competition. For ES401, high viscosity activates T6SS expression and neutral/acidic pH promotes cell-cell contact for killing, and this pH-dependent phenotype was conserved in the majority of T6SS-encoding strains examined. We also identified a subset of V. fischeri isolates that engaged in T6SS-mediated competition at high viscosity under both planktonic and host-like pH conditions. T6SS phylogeny revealed that strains with pH-dependent phenotypes cluster together to form a subclade within the pH-independent strains, suggesting that V. fischeri may have recently evolved to limit competition to the host niche. IMPORTANCE Bacteria have evolved diverse strategies to compete for limited space and resources. Because these mechanisms can be costly to use, their expression and function are often restricted to specific environments where the benefits outweigh the costs. However, little is known about the specific cues that modulate competitive mechanisms as bacterial symbionts transition between free-living and host habitats. Here, we used the bioluminescent squid and fish symbiont Vibrio fischeri to probe for host and environmental conditions that control interbacterial competition via the type VI secretion system. Our findings identify a new host-specific cue that promotes competition among many but not all V. fischeri isolates, underscoring the utility of studying multiple strains to reveal how competitive mechanisms may be differentially regulated among closely related populations as they evolve to fill distinct niches.