Coral bleaching caused by ocean warming is leading to worldwide coral decline. The physiological processes underlying this ecological event are still incompletely understood, although previous research has suggested oxidative stress as major player in the impairment of symbiont thylakoid membranes and in symbiosis breakdown. Lipids are interesting targets of investigation, given their susceptibility to thermal and oxidative stresses. Here, an untargeted lipidomic approach was employed to examine changes in lipidome and pigments of three coral reef symbionts (Symbiodiniaceae) after a heat shock in in vitro experiments. The acute thermal stress induced species-specific changes in lipidome and pigments compositions of both heat sensitive and tolerant symbionts. Heat sensitivity was characterized by a steep and steady decline in cell densities over time (4 and 240 h after heat shock). At the membrane level, heat sensitive symbiont displayed a quantitative decrease in glycolipids linked to polyunsaturated fatty acids, followed by enrichment in oxidized lipids and sphingolipids. Despite showing distinct adaptations, the two heat tolerant symbionts were characterized by the preservation of membrane lipids after heat shock, particularly glycolipids. This finding suggests the action of powerful antioxidant systems, preventing the escalation of oxidized lipids concentration in thylakoid membranes under thermal stress. Although limited by the examination of free-living symbionts, our study provides a solid baseline for the investigation of lipidome and pigments alterations of Symbiodiniaceae in response to heat stress. Novel potential lipid biomarkers linked to thermal stress are suggested. In particular, oxidized lipids—which are implicated in coral symbiosis establishment and breakdown—appear as attractive targets for further research.

中文翻译：

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珊瑚礁共生体的热可塑性与其脂质组组成的重大变化有关

海洋变暖引起的珊瑚白化正在导致全球珊瑚数量减少。尽管先前的研究表明氧化应激是共生类囊体膜受损和共生破坏的主要参与者，但这一生态事件背后的生理过程仍未完全了解。考虑到脂质对热和氧化应激的敏感性，脂质是有趣的研究目标。在这里，采用非靶向脂质组学方法来检查体外热休克后三种珊瑚礁共生体（Symbiodiniaceae）脂质组和色素的变化实验。急性热应激导致热敏感和耐受共生体的脂质组和色素组成发生物种特异性变化。热敏感性的特征是细胞密度随时间急剧而稳定地下降（热激后 4 和 240 小时）。在膜水平上，热敏共生体显示与多不饱和脂肪酸相关的糖脂数量减少，然后富集氧化脂质和鞘脂。尽管表现出明显的适应性，但这两种耐热共生体的特征在于热休克后膜脂的保存，特别是糖脂。这一发现表明了强大的抗氧化系统的作用，可防止热应激下类囊体膜中氧化脂质浓度的升高。尽管受到自由生活共生体检查的限制，但我们的研究为研究共生菌科响应热应激的脂质组和色素变化提供了坚实的基线。提出了与热应激相关的新型潜在脂质生物标志物。特别是，与珊瑚共生建立和分解有关的氧化脂质似乎是进一步研究的有吸引力的目标。