Divergent paths in the evolutionary history of maternally transmitted clam symbionts
Divergent paths in the evolutionary history of maternally transmitted clam symbionts
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DOI：
10.1098/rspb.2021.2137
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发表时间：
2022-03-09
影响因子：
4.7
通讯作者：
Young，C. Robert
中科院分区：
文献类型：
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作者：
Perez，Maeva;Breusing，Corinna;Young，C. Robert
细菌内共生菌的垂直传播伴随着几乎不可逆转的基因丢失，导致基因组大小的进行性缩小。虽然基因组减少的进化过程在一些陆地共生体中得到了很好的描述，但在海洋系统中了解较少，因为海洋系统很少观察到垂直传播。深海囊泡菌和化学合成的伽马蛋白细菌之间的联系是海洋中母体遗传共生的一个例子。在这里，我们通过比较15个有代表性的共生体基因组(1.017-1.586 Mb)与密切相关的细菌和宿主线粒体的基因组，评估了漂移、重组和选择对两个现存的泡囊菌类共生体基因组进化的贡献。我们的分析表明，漂移是推动泡囊菌类共生体基因组进化的重要力量，尽管选择和种间重组似乎对于维持共生体功能的完整性和创造不同的基因保守模式至关重要。值得注意的是，这两个共生体在硫化物生理、无氧呼吸和对环境维生素B12的依赖性方面具有假定的功能差异，这可能反映了每个共生体对不同生态生境的适应。总体而言，这些结果有助于我们理解在垂直传播的共生体中塑造还原基因组进化的生态进化过程。
Vertical transmission of bacterial endosymbionts is accompanied by virtually irreversible gene loss that results in a progressive reduction in genome size. While the evolutionary processes of genome reduction have been well described in some terrestrial symbioses, they are less understood in marine systems where vertical transmission is rarely observed. The association between deep-sea vesicomyid clams and chemosynthetic Gammaproteobacteria is one example of maternally inherited symbioses in the ocean. Here, we assessed the contributions of drift, recombination and selection to genome evolution in two extant vesicomyid symbiont clades by comparing 15 representative symbiont genomes (1.017–1.586 Mb) to those of closely related bacteria and the hosts' mitochondria. Our analyses suggest that drift is a significant force driving genome evolution in vesicomyid symbionts, though selection and interspecific recombination appear to be critical for maintaining symbiont functional integrity and creating divergent patterns of gene conservation. Notably, the two symbiont clades possess putative functional differences in sulfide physiology, anaerobic respiration and dependency on environmental vitamin B12, which probably reflect adaptations to different ecological habitats available to each symbiont group. Overall, these results contribute to our understanding of the eco-evolutionary processes shaping reductive genome evolution in vertically transmitted symbioses.