Strict host-symbiont cospeciation and reductive genome evolution in insect gut bacteria.
Strict host-symbiont cospeciation and reductive genome evolution in insect gut bacteria.
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DOI：
10.1371/journal.pbio.0040337
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发表时间：
2006-10
期刊：
影响因子：
9.8
通讯作者：
Fukatsu T
中科院分区：
文献类型：
--
作者：
Hosokawa T;Kikuchi Y;Nikoh N;Shimada M;Fukatsu T
宿主共生体共物种形成和还原基因组进化已被确定在专性胞内昆虫共生体，但没有这样的例子已经确定从胞外的。在这里，我们首先报告了这种情况下，在家庭Plataspidae，其中一个特定的肠道细菌垂直传播通过“共生体胶囊。”在所有的plataspid物种，女性产生共生体胶囊产卵后，他们的肠道表现出专门的性状胶囊生产。系统发育分析表明，扁虫共生体与蚜虫专性胞内共生体Buchnera为姐妹群，构成γ-变形菌门的一个独立类群。共生体的去除导致昆虫生长迟缓、死亡和不育。宿主共生发生与共生体共生发生完全一致，表明尽管存在胞外关联，但宿主-共生体存在严格的物种形成。共生体表现出AT偏向的核苷酸组成，加速分子进化，并减少基因组大小，已观察到专性胞内昆虫共生体。这些研究结果表明，不是细胞内的条件本身，但垂直传播的共生体的群体遗传属性可能是负责这些昆虫共生体的独特的遗传性状。我们建议命名为“石川贝”的plataspid共生体。其中宿主-共生体协会可以很容易地操纵的plataspid臭虫，提供了一个新的系统，使实验方法，以前未触及的方面的昆虫-微生物共生。此外，比较分析的姐妹集团，细胞内的Buchnera和细胞外的Ishikawaella，将导致洞察不同的共生生活方式如何影响他们的基因组进化。昆虫肠道共生体中宿主共生的证据表明，长期的垂直传播和种群结构是驱动昆虫营养共生体特征基因组变化的核心力量。
Host-symbiont cospeciation and reductive genome evolution have been identified in obligate endocellular insect symbionts, but no such example has been identified from extracellular ones. Here we first report such a case in stinkbugs of the family Plataspidae, wherein a specific gut bacterium is vertically transmitted via “symbiont capsule.” In all of the plataspid species, females produced symbiont capsules upon oviposition and their gut exhibited specialized traits for capsule production. Phylogenetic analysis showed that the plataspid symbionts constituted a distinct group in the γ-Proteobacteria, whose sister group was the aphid obligate endocellular symbionts Buchnera. Removal of the symbionts resulted in retarded growth, mortality, and sterility of the insects. The host phylogeny perfectly agreed with the symbiont phylogeny, indicating strict host-symbiont cospeciation despite the extracellular association. The symbionts exhibited AT-biased nucleotide composition, accelerated molecular evolution, and reduced genome size, as has been observed in obligate endocellular insect symbionts. These findings suggest that not the endocellular conditions themselves but the population genetic attributes of the vertically transmitted symbionts are probably responsible for the peculiar genetic traits of these insect symbionts. We proposed the designation “Candidatus Ishikawaella capsulata” for the plataspid symbionts. The plataspid stinkbugs, wherein the host-symbiont associations can be easily manipulated, provide a novel system that enables experimental approaches to previously untouched aspects of the insect-microbe mutualism. Furthermore, comparative analyses of the sister groups, the endocellular Buchnera and the extracellular Ishikawaella, would lead to insights into how the different symbiotic lifestyles have affected their genomic evolution. Evidence of host-symbiont cospeciation in an insect gut symbiont suggests that long-term vertical transmission and population structure are central forces driving the genomic changes characteristic of insect nutritional symbionts.
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