近日，美国普林斯顿大学Mohamed S. Donia研究团队发现，在一个由三种生物所构成的海洋共生体中，存在一个能够产生防御性毒素的微生物工厂。该项研究成果发表在2019年6月14日出版的《科学》上。

研究人员发现了一个由三种生物组成的海洋共生体，其中一种细胞内的共生细菌（Candidatus Endobryopsis kahalalidefaciens）利用一系列的生物合成酶将简单的底物催化为大量的复杂分子（kahalalides）作为宿主（即一种羽藻Bryopsis）对抗猎食者的化学防御。这些kahalalides毒素随后被第三个共生者（一种草食性软体动物Elysia rufescens）获取并同样用来作为防御。“Ca. E. kahalalidefaciens”细菌丧失了大量关键的独立生存技能，转而变成了一个专门产生kahalalide的工厂。因此，一种细菌、一种海藻和一种动物之间的互动体现出了复杂共生体进化中化学防御的重要性。

据介绍，在自然生态系统中，抵抗猎食者的化学防御广泛存在。有时不同种类的生物体会共用同一道化学防线。
 

附：英文原文

Title: A microbial factory for defensive kahalalides in a tripartite marine symbiosis

Author: Jindong Zan, Zhiyuan Li, Ma. Diarey Tianero, Jeanette Davis, Russell T. Hill, Mohamed S. Donia

Issue&Volume: VOL 364, ISSUE 6445,14 JUNE 2019

Abstract: Chemical defense against predators is widespread in natural ecosystems. Occasionally, taxonomically distant organisms share the same defense chemical. Here, we describe an unusual tripartite marine symbiosis, in which an intracellular bacterial symbiont (“Candidatus Endobryopsis kahalalidefaciens”) uses a diverse array of biosynthetic enzymes to convert simple substrates into a library of complex molecules (the kahalalides) for chemical defense of the host, the alga Bryopsis sp., against predation. The kahalalides are subsequently hijacked by a third partner, the herbivorous mollusk Elysia rufescens, and employed similarly for defense. “Ca. E. kahalalidefaciens” has lost many essential traits for free living and acts as a factory for kahalalide production. This interaction between a bacterium, an alga, and an animal highlights the importance of chemical defense in the evolution of complex symbioses.

DOI: DOI: 10.1126/science.aaw6732

Source: https://science.sciencemag.org/content/364/6445/eaaw6732