Cyanobacteria are the only prokaryotes to have evolved oxygenic photosynthesis paving the way for complex life. Studying the evolution and ecological niche of cyanobacteria and their ancestors is crucial for understanding the intricate dynamics of biosphere evolution. These organisms frequently deal with environmental stressors such as salinity and drought, and they employ compatible solutes as a mechanism to cope with these challenges. Compatible solutes are small molecules that help maintain cellular osmotic balance in high salinity environments, such as marine waters. Their production plays a crucial role in salt tolerance, which, in turn, influences habitat preference. Among the five known compatible solutes produced by cyanobacteria (sucrose, trehalose, glucosylglycerol, glucosylglycerate, and glycine betaine), their synthesis varies between individual strains. In this study, we work in a Bayesian stochastic mapping framework, integrating multiple sources of information about compatible solute biosynthesis in order to predict the ancestral habitat preference of Cyanobacteria. Through extensive model selection analyses and statistical tests for correlation, we identify glucosylglycerol and glucosylglycerate as the most significantly correlated with habitat preference, while trehalose exhibits the weakest correlation. Additionally, glucosylglycerol, glucosylglycerate, and glycine betaine show high loss/gain rate ratios, indicating their potential role in adaptability, while sucrose and trehalose are less likely to be lost due to their additional cellular functions. Contrary to previous findings, our analyses predict that the last common ancestor of Cyanobacteria (living at around 3180 Ma) had a 97% probability of a high salinity habitat preference and was likely able to synthesise glucosylglycerol and glucosylglycerate. Nevertheless, cyanobacteria likely colonized low-salinity environments shortly after their origin, with an 89% probability of the first cyanobacterium with low-salinity habitat preference arising prior to the Great Oxygenation Event (2460 Ma). Stochastic mapping analyses provide evidence of cyanobacteria inhabiting early marine habitats, aiding in the interpretation of the geological record. Our age estimate of ~2590 Ma for the divergence of two major cyanobacterial clades (Macro- and Microcyanobacteria) suggests that these were likely significant contributors to primary productivity in marine habitats in the lead-up to the Great Oxygenation Event, and thus played a pivotal role in triggering the sudden increase in atmospheric oxygen.

中文翻译：

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随机特征图谱、贝叶斯模型选择和生物合成途径为蓝藻栖息地偏好的演变提供了新的视角


蓝细菌是唯一进化出含氧光合作用的原核生物，为复杂的生命铺平了道路。研究蓝藻及其祖先的进化和生态位对于理解生物圈进化的复杂动力学至关重要。这些生物经常处理盐度和干旱等环境压力源，它们采用相容溶质作为应对这些挑战的机制。相容溶质是小分子，有助于在高盐度环境（如海水）中维持细胞渗透平衡。它们的生产在耐盐性中起着至关重要的作用，这反过来又会影响栖息地的偏好。在蓝细菌产生的五种已知相容溶质（蔗糖、海藻糖、葡萄糖基甘油、葡萄糖基甘油酸酯和甘氨酸甜菜碱）中，它们的合成因菌株而异。在这项研究中，我们在贝叶斯随机映射框架中工作，整合了有关相容溶质生物合成的多个信息来源，以预测蓝细菌的祖先栖息地偏好。通过广泛的模型选择分析和相关性统计检验，我们确定葡萄糖甘油和葡萄糖甘油酸酯与栖息地偏好的相关性最显著，而海藻糖的相关性最弱。此外，葡萄糖甘油、葡萄糖甘油酸酯和甘氨酸甜菜碱显示出高损失/增益率比，表明它们在适应性中的潜在作用，而蔗糖和海藻糖由于其额外的细胞功能而不太可能丢失。 与以前的发现相反，我们的分析预测蓝细菌的最后一个共同祖先（生活在 3180 马 左右）具有高盐度栖息地偏好的概率为 97%，并且可能能够合成葡萄糖甘油和葡萄糖甘油酸酯。尽管如此，蓝藻可能在起源后不久就在低盐度环境中定植，在大氧化事件（2460 马）之前出现第一个具有低盐度栖息地偏好的蓝细菌的可能性为 89%。随机制图分析提供了蓝藻栖息在早期海洋栖息地的证据，有助于解释地质记录。我们对两个主要蓝藻分支（宏蓝藻和微蓝藻）分化的~2590 马的年龄估计表明，在大氧化事件之前，它们可能是海洋栖息地初级生产力的重要贡献者，因此在触发大气氧气的突然增加中起了关键作用。