Olaso Caleb-Matthew, Viliunas Joani, McFall-Ngai Margaret
Pacific Biosciences Research Center, University of Hawai'i at Mānoa, Honolulu, HI, USA.
Division of Biosphere Sciences and Engineering, Carnegie Institution for Science, Pasadena, CA, USA.
Symbiosis. 2022 May;87(1):31-43. doi: 10.1007/s13199-022-00855-y. Epub 2022 Aug 6.
In symbioses established through horizontal transmission, evolution has selected for mechanisms that promote the recruitment of symbionts from the environment. Using the binary association between the Hawaiian bobtail squid, , and its symbiont, , we explored the first step of symbiont enrichment around sites where cells will enter host tissues. Earlier studies of the system had shown that, within minutes of hatching in natural seawater, ciliated epithelia of the nascent symbiotic tissue secrete a layer of mucus in response to exposure to the cell-wall biomolecule peptidoglycan (PGN) from non-specific bacterioplankton. We hypothesized that a peptidoglycan recognition protein, EsPGRP4, is the receptor that mediates host mucus secretion by sensing the environmental PGN; earlier studies of this protein family had shown that this is the only member predicted to behave as a membrane receptor. Immunocytochemistry localized EsPGRP4 to the superficial ciliated fields of the juvenile organ. We found that production of EsPGRP4 increased over the first 48 h after hatching if the light organ remained uncolonized. When colonized by , the levels of the protein in light-organ tissue remained similar to that of hatchling organs. Pharmacologically curing the initially colonized light organ with antibiotics resulted in return of EsPGRP4 production to levels similar to light organs that had remained uncolonized since hatching. Furthermore, we found that preincubation of the tissues with an EsPGRP4 antibody decreased light organ mucus production and colonization. These findings provide evidence of an innate mechanism that underlies a crucial first step in the horizontal recruitment of bacterial symbionts.
在通过水平传播建立的共生关系中，进化选择了促进从环境中招募共生体的机制。利用夏威夷短尾乌贼与其共生体之间的二元关联，我们探索了共生体在细胞进入宿主组织的部位周围富集的第一步。该系统早期的研究表明，在天然海水中孵化后的几分钟内，新生共生组织的纤毛上皮会因接触来自非特异性浮游细菌的细胞壁生物分子肽聚糖（PGN）而分泌一层黏液。我们假设一种肽聚糖识别蛋白EsPGRP4是通过感知环境中的PGN来介导宿主黏液分泌的受体；对该蛋白家族早期的研究表明，这是预测会表现为膜受体的唯一成员。免疫细胞化学将EsPGRP4定位到幼体器官的表面纤毛区域。我们发现，如果发光器官未被定殖，孵化后最初48小时内EsPGRP4的产生会增加。当被定殖时，发光器官组织中该蛋白的水平与孵化幼体器官的水平相似。用抗生素对最初定殖的发光器官进行药物清除后，EsPGRP4的产生恢复到与孵化后一直未被定殖的发光器官相似的水平。此外，我们发现用EsPGRP4抗体对组织进行预孵育会减少发光器官的黏液产生和定殖。这些发现为细菌共生体水平招募关键第一步背后的先天机制提供了证据。
