Coral bleaching, i.e., the loss of photosynthetic algal endosymbionts, caused by ocean warming is now among the main factors driving global reef decline, making the elucidation of factors that contribute to thermotolerance important. Recent studies implicate high salinity as a contributing factor in cnidarians, potentially explaining the high thermotolerance of corals from the Arabian Seas. Here we characterized bacterial community composition under heat stress at different salinities using the coral model Aiptasia. Exposure of two Aiptasia host-algal symbiont pairings (H2-SSB01 and CC7-SSA01) to ambient (25°C) and heat stress (34°C) temperatures at low (36 PSU), intermediate (39 PSU), and high (42 PSU) salinities showed that bacterial community composition at high salinity was significantly different, concomitant with reduced bleaching susceptibility in H2-SSB01, not observed in CC7-SSA01. Elucidation of bacteria that showed increased relative abundance at high salinity, irrespective of heat stress, revealed candidate taxa that could potentially contribute to the observed increased thermotolerance. We identified 4 (H2-SSB01) and 3 (CC7-SSA01) bacterial taxa belonging to the orders Alteromonadales (1 OTU), Oligoflexales (1 OTU), Rhizobiales (2 OTUs), and Rhodobacterales (2 OTUs), suggesting that only few bacterial taxa are potential contributors to an increase in thermal tolerance at high salinities. These taxa have previously been implicated in nitrogen and DMSP cycling, processes that are considered to affect thermotolerance. Our study demonstrates microbiome restructuring in symbiotic cnidarians under heat stress at different salinities. As such, it underlines how host-associated bacterial communities adapt to prevailing environmental conditions with putative consequences for the environmental stress tolerance of the emergent metaorganism.

中文翻译：

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珊瑚模型 Aiptasia 中的盐度传递耐热性伴随着细菌微生物组的明显变化

由海洋变暖引起的珊瑚白化，即光合藻类内共生体的丧失，现在是导致全球珊瑚礁减少的主要因素之一，因此阐明导致耐热性的因素很重要。最近的研究表明，高盐度是刺胞动物的一个促成因素，这可能解释了阿拉伯海珊瑚的高耐热性。在这里，我们使用珊瑚模型 Aiptasia 表征了不同盐度下热应激下的细菌群落组成。将两种 Aiptasia 宿主-藻类共生体配对（H2-SSB01 和 CC7-SSA01）暴露于环境 (25°C) 和热应力 (34°C) 的低温 (36 PSU)、中 (39 PSU) 和高温 ( 42 PSU) 盐度表明高盐度下细菌群落组成存在显着差异，伴随着 H2-SSB01 中漂白敏感性降低，在 CC7-SSA01 中未观察到。阐明在高盐度下相对丰度增加的细菌，无论热应激如何，揭示了可能有助于观察到的耐热性增加的候选分类群。我们确定了属于交替单胞菌目 (1 OTU)、寡屈目 (1 OTU)、根瘤菌目 (2 OTU) 和红杆菌目 (2 OTU) 的 4 个 (H2-SSB01) 和 3 个 (CC7-SSA01) 细菌分类群，表明只有少数细菌分类群是提高高盐度耐热性的潜在因素。这些分类群以前曾与氮和 DMSP 循环有关，这些过程被认为会影响耐热性。我们的研究表明，在不同盐度的热应激下，共生刺胞动物的微生物组重组。