The picocyanobacteria genera Prochlorococcus and Synechococcus play a significant role globally, dominating the primary production in warm and oligotrophic tropical and subtropical areas, which represent the largest oceanic ecosystem. Genomic studies have revealed high microdiversity within these genera. It is anticipated that ocean warming may cause decreased biodiversity in marine tropical areas, as increasing temperatures may lead to the development of a new thermal niche in these regions. Thus, our study aimed to characterize the microdiversity of picocyanobacteria in the Red Sea, one of the warmest oligotrophic seas on the planet, which is experiencing warming at a rate that exceeds the global average. We identified picocyanobacteria microdiversity in the open waters of the Eastern Red Sea basin, where seawater temperatures ranged from 22.2 to 32.4°C throughout the water column (from surface to 160 m depth). Both Prochlorococcus and Synechococcus populations were characterized to deep taxonomic levels, applying amplicon sequencing targeting the petB gene, revealing up to 15 different (sub)clades. Synechococcus dominated the basin, representing an average of 68.8% of the total reads assigned to both cyanobacteria. The subclade Synechococcus IIa and Prochlorococcus clade HLII were ubiquitous in the water column of the Eastern Red Sea basin, representing 73% and 56% of the Synechococcus and Prochlorococcus assigned reads, respectively. Maximum cyanobacteria richness was observed at approximately 27.5°C, declining at higher and lower temperatures (polynomial fit, R2 = 0.2, p<0.0001). Synechococcus IIa dominated in the warmest surface waters (>30°C) of the Red Sea, displacing other (sub)clades to more saline and nutrient-poor waters, thereby reducing community diversity (polynomial fit, R2 = 0.77, p<0.0001). Our study contributes to identifying changes in picocyanobacterial diversity when exposed to temperatures exceeding current oceanic thermal limits, through the analysis of Red Sea communities already inhabiting such higher-temperature niches.

中文翻译：

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海水温度升高导致海洋变暖中关键蓝藻（聚球藻和原绿球藻）的多样性


微微蓝藻属原绿球藻属和聚球蓝藻属在全球发挥着重要作用，在代表最大海洋生态系统的温暖和贫营养热带和亚热带地区的初级生产中占主导地位。基因组研究揭示了这些属内的高度微观多样性。预计海洋变暖可能会导致海洋热带地区的生物多样性减少，因为气温升高可能会导致这些地区出现新的热生态位。因此，我们的研究旨在表征红海中微微蓝细菌的微观多样性，红海是地球上最温暖的寡营养海洋之一，其变暖速度超过了全球平均水平。我们在红海盆地东部的开放水域中发现了微微蓝细菌的微多样性，该地区整个水体（从表面到 160 m 深度）的海水温度范围为 22.2 至 32.4°C。应用针对 petB 基因的扩增子测序，对原绿球藻和聚球藻种群进行了深层分类水平的表征，揭示了多达 15 个不同的（亚）分支。聚球藻在该盆地中占主导地位，平均占分配给两种蓝藻的总读数的 68.8%。聚球藻 IIa 分支和原绿球藻 HLII 分支在红海东部盆地的水体中普遍存在，分别占聚球藻和原绿球藻分配读数的 73% 和 56%。在大约 27.5°C 时观察到蓝藻丰富度最大，随温度升高和降低而下降（多项式拟合，R2 = 0.2，p<0.0001）。 聚球藻 IIa 在红海最温暖的表层水域 (>30°C) 中占主导地位，将其他（子）分支转移到含盐量更高和营养贫乏的水域，从而降低了群落多样性（多项式拟合，R2 = 0.77，p<0. 0001）。我们的研究有助于通过分析已经栖息在这种较高温度生态位的红海群落，确定暴露于超过当前海洋热极限的温度时微微蓝藻多样性的变化。