蓝细菌是唯一进化出氧气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。这些生物经常应对环境压力,如盐度和干旱,他们采用相容的溶质作为应对这些挑战的机制。相容溶质是有助于在高盐度环境中维持细胞渗透平衡的小分子,比如海洋水域。它们的生产在耐盐性中起着至关重要的作用,which,反过来,影响栖息地偏好。在蓝细菌产生的五种已知的相容性溶质中(蔗糖,海藻糖,葡萄糖基甘油,葡萄糖基甘油酯,和甘氨酸甜菜碱),它们的合成在各个菌株之间变化。在这项研究中,我们在贝叶斯随机映射框架中工作,整合有关相容性溶质生物合成的多种信息来源,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的统计检验,我们确定葡萄糖基甘油和葡萄糖基甘油与栖息地偏好最显著相关,而海藻糖表现出最弱的相关性。此外,葡萄糖基甘油,葡萄糖基甘油酯,和甘氨酸甜菜碱显示高的损失/增益比,表明它们在适应性方面的潜在作用,而蔗糖和海藻糖由于其额外的细胞功能而不太可能丢失。与之前的发现相反,我们的分析预测,蓝细菌的最后一个共同祖先(生活在3180Ma左右)具有高盐度栖息地偏好的97%的可能性,并且可能能够合成葡萄糖基甘油和葡萄糖基甘油。然而,蓝藻可能在其起源后不久就定居在低盐度环境中,在大氧合事件(2460Ma)之前,第一个具有低盐度栖息地偏好的蓝细菌的概率为89%。随机作图分析提供了蓝细菌居住在早期海洋栖息地的证据,协助解释地质记录。对于两个主要的蓝细菌进化枝(宏观和微蓝细菌)的差异,我们的年龄估计为〜2590Ma,这表明在大氧化事件之前,这些可能是海洋生境初级生产力的重要贡献者,因此在引发大气氧气突然增加方面发挥了关键作用。
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.