Allying with armored snails: the complete genome of gammaproteobacterial endosymbiont
Allying with armored snails: the complete genome of gammaproteobacterial endosymbiont
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DOI：
10.1038/ismej.2013.131
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发表时间：
2014-01-01
期刊：
影响因子：
11
通讯作者：
Takai, Ken
中科院分区：
文献类型：
--
作者：
Nakagawa, Satoshi;Shimamura, Shigeru;Takai, Ken
深海喷口拥有各种动物的密集种群，这些动物有其特定的共生细菌。鳞足腹足类是一种覆盖在其足两侧的矿化鳞片的蜗牛，在其扩大的食管腺中有一种γ-变形菌内共生体，在其鳞片表面上有多种多样的外生体。在这项研究中，我们报告了全基因组测序的γ-变形菌内共生体。内共生体基因组显示与正在进行的基因组减少相一致的特征，例如大比例的假基因和插入元件。该基因组编码深海喷口化能自养生物中常见的功能，如硫氧化和碳固定。稳定碳同位素（C-13）标记实验证实了内共生体的化能自养。该基因组还包括一个完整的氢化酶基因簇，该基因簇可能是从遗传学上遥远的细菌水平转移而来的。值得注意的发现包括鞭毛组装基因的存在和转录，通过鞭毛组装，蛋白质可能从细菌输出到宿主。蜗牛个体的共生体表现出极端的遗传同质性，在19个不同的基因（共13 810个位置），只有两个同义的变化，确定了32个个体腹足类从一个单一的殖民地在同一时间。内共生体极低的遗传个体性可能反映了寄主对共生体的严格选择阻止了水平传播共生体小种群的随机遗传漂变。这项研究是第一个完整的腹足类内共生体的基因组分析，并提供了一个机会，研究基因组进化在最近进化的内共生体。
Deep-sea vents harbor dense populations of various animals that have their specific symbiotic bacteria. Scaly-foot gastropods, which are snails with mineralized scales covering the sides of its foot, have a gammaproteobacterial endosymbiont in their enlarged esophageal glands and diverse epibionts on the surface of their scales. In this study, we report the complete genome sequencing of gammaproteobacterial endosymbiont. The endosymbiont genome displays features consistent with ongoing genome reduction such as large proportions of pseudogenes and insertion elements. The genome encodes functions commonly found in deep-sea vent chemoautotrophs such as sulfur oxidation and carbon fixation. Stable carbon isotope (C-13)-labeling experiments confirmed the endosymbiont chemoautotrophy. The genome also includes an intact hydrogenase gene cluster that potentially has been horizontally transferred from phylogenetically distant bacteria. Notable findings include the presence and transcription of genes for flagellar assembly, through which proteins are potentially exported from bacterium to the host. Symbionts of snail individuals exhibited extreme genetic homogeneity, showing only two synonymous changes in 19 different genes (13 810 positions in total) determined for 32 individual gastropods collected from a single colony at one time. The extremely low genetic individuality in endosymbionts probably reflects that the stringent symbiont selection by host prevents the random genetic drift in the small population of horizontally transmitted symbiont. This study is the first complete genome analysis of gastropod endosymbiont and offers an opportunity to study genome evolution in a recently evolved endosymbiont.