Ecologie Systématique Evolution, CNRS, Université Paris-Sud, AgroParisTech, Université Paris-Saclay, Orsay, France.
Institut de Biologie Intégrative de la Cellule, CNRS, Université Paris-Sud, Université Paris-Saclay, Orsay, France.
Nat Ecol Evol. 2018 Nov;2(11):1700-1708. doi: 10.1038/s41559-018-0683-3. Epub 2018 Oct 8.
Phototrophic microbial mats dominated terrestrial ecosystems for billions of years, largely causing, through cyanobacterial oxygenic photosynthesis, but also undergoing, the Great Oxidation Event approximately 2.5 billion years ago. Taking a space-for-time approach based on the universality of core metabolic pathways expressed at ecosystem level, we studied gene content and co-occurrence networks in high-diversity metagenomes from spatially close microbial mats along a steep redox gradient. The observed functional shifts suggest that anoxygenic photosynthesis was present but not predominant under early Precambrian conditions, being accompanied by other autotrophic processes. Our data also suggest that, in contrast to general assumptions, anoxygenic photosynthesis largely expanded in parallel with the subsequent evolution of oxygenic photosynthesis and aerobic respiration. Finally, our observations might represent space-for-time evidence that the Wood-Ljungdahl carbon fixation pathway dominated phototrophic mats in early ecosystems, whereas the Calvin cycle probably evolved from pre-existing variants before becoming the dominant contemporary form of carbon fixation.
光养微生物垫主导陆地生态系统数十亿年，主要通过蓝细菌的有氧光合作用引起，但也经历了大约 25 亿年前的大氧化事件。基于在生态系统水平上表达的核心代谢途径的普遍性，我们采用了一种空间替代时间的方法，研究了来自沿陡峭氧化还原梯度的空间上接近的微生物垫的高多样性宏基因组中的基因含量和共同发生网络。观察到的功能转变表明，在早期前寒武纪条件下，虽然存在但不是主要的厌氧光合作用，伴随着其他自养过程。我们的数据还表明，与一般假设相反，厌氧光合作用在很大程度上与随后的有氧光合作用和需氧呼吸的进化平行扩展。最后，我们的观察结果可能代表了空间替代时间的证据，表明伍德-吕根达尔碳固定途径在早期生态系统中主导光养垫，而卡尔文循环可能是在成为当代主要碳固定形式之前从现有变体进化而来的。
