近日，上海交通大学王寅炤、中国科学院地质与地球物理研所李金华和西北大学张兴亮的团队合作发现，寒武纪微体化石Qingjiangonema揭示了硫酸盐还原细菌和地表氧化的共同进化。相关论文于2024年3月2日发表在《科学通报》杂志上。

研究团队报道了一种新的微体化石—Qingjiangonema cambria，它来自于清江生物群的约5.18亿年前的黑色页岩。Qingjiangonema由数百个充满的等形和等维黄铁矿微晶组成的长丝状结构，具有轻硫同位素组成。多项证据表明，Qingjiangonema是一种硫酸盐还原菌，其细胞组织模式与脱硫菌门中的丝状细菌形式相似，包括硫酸盐还原Desulfonema和硫化物氧化cable菌。系统基因组学分析证实了Desulfonema和cable细菌中多细胞性的独立起源。

分子钟分析表明，Desulfobacterota（包括大多数硫酸盐还原分类群）在24.1亿年前的古元古代大氧化事件中出现分化，而cable细菌a在5.6亿年前的新元古代氧化事件中或之后出现分化。综上所述，该研究团队将Qingjiangonema解释为一种多细胞硫酸盐还原微体化石，并提出cable细菌是从多细胞丝状物演变而来的硫酸盐还原祖先。研究推断，Desulfobacterota的多样化和cable细菌的起源可能是对地球历史上氧化事件的反应。

据悉，硫酸盐还原是维持海洋和陆地生态系统生物地球化学循环的重要代谢。硫酸盐还原剂完全是原核生物、系统发育多样，可能在地球历史的早期就进化了。然而，它们的起源令人难以捉摸且缺乏明确的化石证据。

附：英文原文

Title: The Cambrian microfossil Qingjiangonema reveals the co-evolution of sulfate-reducing bacteria and the oxygenation of Earth’s surface

Author: Linhao Cui, Kelei Zhu, Ruiyun Li, Chao Chang, Laiyuan Wu, Wei Liu, Dongjing Fu, Peiyu Liu, Hao Qiu, Guoqiang Tang, Qili Li, Robert R. Gaines, Yuxin Tao, Yinzhao Wang, Jinhua Li, Xingliang Zhang

Issue&Volume: 2024/03/02

Abstract: Sulfate reduction is an essential metabolism that maintains biogeochemical cycles in marine and terrestrial ecosystems. Sulfate reducers are exclusively prokaryotic, phylogenetically diverse, and may have evolved early in Earth’s history. However, their origin is elusive and unequivocal fossils are lacking. Here we report a new microfossil, Qingjiangonema cambria, from ～518-million-year-old black shales that yield the Qingjiang biota. Qingjiangonema is a long filamentous form comprising hundreds of cells filled by equimorphic and equidimensional pyrite microcrystals with a light sulfur isotope composition. Multiple lines of evidence indicate Qingjiangonema was a sulfate-reducing bacterium that exhibits similar patterns of cell organization to filamentous forms within the phylum Desulfobacterota, including the sulfate-reducing Desulfonema and sulfide-oxidizing cable bacteria. Phylogenomic analyses confirm separate, independent origins of multicellularity in Desulfonema and in cable bacteria. Molecular clock analyses infer that the Desulfobacterota, which encompass a majority of sulfate-reducing taxa, diverged ～2.41 billion years ago during the Paleoproterozoic Great Oxygenation Event, while cable bacteria diverged ～0.56 billion years ago during or immediately after the Neoproterozoic Oxygenation Event. Taken together, we interpret Qingjiangonema as a multicellular sulfate-reducing microfossil and propose that cable bacteria evolved from a multicellular filamentous sulfate-reducing ancestor. We infer that the diversification of the Desulfobacterota and the origin of cable bacteria may have been responses to oxygenation events in Earth’s history.

DOI: 10.1016/j.scib.2024.03.001

Source: https://www.sciencedirect.com/science/article/pii/S2095927324001452