A major debate in evolutionary biology is whether virulence is maintained as an adaptive trait and/or evolves to non‐virulence. In the environment, virulence traits of non‐obligatory parasites are subjected to diverse selective pressures and trade‐offs. Here, we focus on a population of Vibrio splendidus that displays moderate virulence for oysters. A MARTX (Multifunctional‐autoprocessing repeats‐in‐toxin) and a type‐six secretion system (T6SS) were found to be necessary for virulence toward oysters, while a region (wbe) involved in O‐antigen synthesis is necessary for resistance to predation against amoebae. Gene inactivation within the wbe region had major consequences on the O‐antigen structure, conferring lower immunogenicity, competitive advantage and increased virulence in oyster experimental infections. Therefore, O‐antigen structures that favour resistance to environmental predators result in an increased activation of the oyster immune system and a reduced virulence in that host. These trade‐offs likely contribute to maintaining O‐antigen diversity in the marine environment by favouring genomic plasticity of the wbe region. The results of this study indicate an evolution of V. splendidus towards moderate virulence as a compromise between fitness in the oyster as a host, and resistance to its predators in the environment.

中文翻译：

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锦绣弧菌O抗原结构：对牡蛎的毒性与对食肉动物的抵抗力之间的权衡

进化生物学中的一个主要争论是毒力是否作为一种适应性特征得以维持和/或演变为非毒力。在环境中，非强制性寄生虫的毒力特性会受到多种选择压力和折衷的影响。在这里，我们集中于Splendidus弧菌对牡蛎显示中等毒性。研究发现，MARTX（多功能自动毒素重复处理）和六型分泌系统（T6SS）对于牡蛎具有毒性，而参与O抗原合成的区域（wbe）对于抵抗捕食是必需的反对变形虫。wbe区域内的基因失活对O抗原结构产生了重要影响，在牡蛎实验感染中赋予较低的免疫原性，竞争优势和增加的毒力。因此，有利于抵抗环境掠食者的O抗原结构会导致牡蛎免疫系统的激活增加，宿主体内的毒力降低。这些折衷可能通过促进wbe地区的基因组可塑性来维护海洋环境中O抗原的多样性。V。由于牡蛎作为宿主的适应能力与对环境中的天敌的抵抗力之间的折衷，因此锦鲤趋向中等毒性。