Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA.
School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
Microbiome. 2023 May 16;11(1):106. doi: 10.1186/s40168-023-01493-2.
Marine symbioses are predominantly established through horizontal acquisition of microbial symbionts from the environment. However, genetic and functional comparisons of free-living populations of symbionts to their host-associated counterparts are sparse. Here, we assembled the first genomes of the chemoautotrophic gammaproteobacterial symbionts affiliated with the deep-sea snail Alviniconcha hessleri from two separate hydrothermal vent fields of the Mariana Back-Arc Basin. We used phylogenomic and population genomic methods to assess sequence and gene content variation between free-living and host-associated symbionts.
Our phylogenomic analyses show that the free-living and host-associated symbionts of A. hessleri from both vent fields are populations of monophyletic strains from a single species. Furthermore, genetic structure and gene content analyses indicate that these symbiont populations are differentiated by vent field rather than by lifestyle.
Together, this work suggests that, despite the potential influence of host-mediated acquisition and release processes on horizontally transmitted symbionts, geographic isolation and/or adaptation to local habitat conditions are important determinants of symbiont population structure and intra-host composition. Video Abstract.
海洋共生关系主要通过从环境中水平获得微生物共生体而建立。然而，自由生活的共生体种群与宿主相关共生体的遗传和功能比较很少。在这里，我们组装了深海蜗牛 Alviniconcha hessleri 的化学自养γ变形菌共生体的第一个基因组，这些共生体来自马里亚纳弧后盆地的两个独立的热液喷口场。我们使用系统发育基因组学和种群基因组学方法来评估自由生活和宿主相关共生体之间的序列和基因含量变异。
我们的系统发育基因组学分析表明，来自两个喷口场的 A. hessleri 的自由生活和宿主相关共生体是来自单一物种的单系菌株的种群。此外，遗传结构和基因含量分析表明，这些共生体种群是由喷口场而不是生活方式来分化的。
总之，这项工作表明，尽管宿主介导的获取和释放过程可能对水平传播的共生体产生影响，但地理隔离和/或对当地栖息地条件的适应是共生体种群结构和宿主内组成的重要决定因素。视频摘要。
