一种当“甩手掌柜”的蠕虫（Symbiosis: doing without）

Symbiosis insights through metagenomic analysis of a microbial consortium

Olavius algarvensis是一种海洋寡毛纲蠕虫，存在于地中海厄尔巴岛沿海浅水沙子中。它们的解剖特征是引人注目的，因为它们不但没有嘴、胃和肠，而且没

有肾管（nephridia），即肾脏一样的器官。消化系统的省略出现在其他动物中，但这种动物是惟一省略了自己的排泄系统以适应共生方式的寄主。现在，生

活在这些蠕虫皮肤下面的共生细菌群落的基因组成已被确定。多源基因组分析揭示了如此多的重要寄主任务何以被外包给了共生体。（Letter p. 950; News

and Views）

Keywords: metagenomic analysis, inability to cultivate most host-associated microbes, metabolic pathway reconstruction

Abstract: Symbioses between bacteria and eukaryotes are ubiquitous, yet our understanding of the interactions driving these associations is hampered by our inability to cultivate most host-associated microbes. Here we use a metagenomic approach to describe four co-occurring symbionts from the marine oligochaete Olavius algarvensis, a worm lacking a mouth, gut and nephridia. Shotgun equencing and metabolic pathway reconstruction revealed that the symbionts are sulphur-oxidizing and sulphate-reducing bacteria, all of which are capable of carbon fixation, thus providing the host with multiple reources of nutrition. Molecular evidence for the uptake and recycling of wormwaste products by the symbionts suggests how the wormcould eliminate its excretory system, an adaptation unique among annelid worms. We propose a model that describes how the versatile metabolism within this symbiotic consortium provides the host with an optimal energy supply as it shuttles between the upper oxic and lower anoxic coastal sediments that it inhabits.