Stefanos Siozios, Pol Nadal-Jimenez, Tal Azagi, Hein Sprong, Crystal L Frost, Steven R Parratt, Graeme Taylor, Laura Brettell, Kwee Chin Liew, Larry Croft, Kayla C King, Michael A Brockhurst, Václav Hypša, Eva Novakova, Alistair C Darby, Gregory D D Hurst
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引用次数: 0
Abstract
Endosymbiosis-where a microbe lives and replicates within a host-is an important contributor to organismal function that has accelerated evolutionary innovations and catalyzed the evolution of complex life. The evolutionary processes associated with transitions to endosymbiosis, however, are poorly understood. Here, we leverage the wide diversity of host-associated lifestyles of the genus Arsenophonus to reveal the complex evolutionary processes that occur during the transition to a vertically transmitted endosymbiotic lifestyle from strains maintained solely by horizontal (infectious) transmission. We compared the genomes of 38 strains spanning diverse lifestyles from horizontally transmitted pathogens to obligate interdependent endosymbionts. Among culturable strains, we observed those with vertical transmission had larger genome sizes than closely related horizontally transmitting counterparts, consistent with evolutionary innovation and the rapid gain of new functions. Increased genome size was a consequence of prophage and plasmid acquisition, including a cargo of type III effectors, alongside the concomitant loss of CRISPR-Cas genome defense systems, enabling mobile genetic element expansion. Persistent endosymbiosis was also associated with loss of type VI secretion, which we hypothesize to be a consequence of reduced microbe-microbe competition. Thereafter, the transition to endosymbiosis with strict vertical inheritance was associated with the expected relaxation of purifying selection, gene pseudogenization, metabolic degradation, and genome reduction. We argue that reduced phage predation in endosymbiotic niches drives the loss of genome defense systems driving rapid genome expansion upon the adoption of endosymbiosis and vertical transmission. This remodeling enables rapid horizontal gene transfer-mediated evolutionary innovation and precedes the reductive evolution traditionally associated with adaptation to endosymbiosis.
内共生--微生物在宿主体内生活和复制--是生物体功能的一个重要因素,它加速了进化创新,催化了复杂生命的进化。然而,人们对过渡到内共生的相关进化过程知之甚少。在这里,我们利用箭毒属与宿主相关的生活方式的广泛多样性,揭示了从仅通过水平(传染性)传播维持的菌株过渡到垂直传播的内共生生活方式过程中发生的复杂进化过程。我们比较了 38 个菌株的基因组,这些菌株的生活方式各不相同,有水平传播的病原体,也有必须相互依存的内生菌。在可培养的菌株中,我们观察到垂直传播菌株的基因组大小大于密切相关的水平传播菌株,这与进化创新和新功能的快速获得是一致的。基因组大小的增加是噬菌体和质粒获取的结果,其中包括III型效应器,同时也是CRISPR-Cas基因组防御系统丧失的结果,这使得移动遗传因子得以扩展。持续的内共生还与 VI 型分泌物的丧失有关,我们推测这是微生物与微生物竞争减少的结果。此后,过渡到严格垂直遗传的内共生,与预期的净化选择放松、基因假基因化、代谢退化和基因组减少有关。我们认为,内共生壁龛中噬菌体捕食的减少导致基因组防御系统的丧失,从而在采用内共生和垂直传播后推动基因组的快速扩张。这种重塑使水平基因转移介导的进化创新得以迅速实现,并先于传统上与适应内共生相关的还原进化。
期刊介绍:
Current Biology is a comprehensive journal that showcases original research in various disciplines of biology. It provides a platform for scientists to disseminate their groundbreaking findings and promotes interdisciplinary communication. The journal publishes articles of general interest, encompassing diverse fields of biology. Moreover, it offers accessible editorial pieces that are specifically designed to enlighten non-specialist readers.