由海德堡海因里希·海涅大学分子进化研究所领导的国际研究团队发现证据表明，地球上最早的自由生活细胞可能独立出现了两次[1]。研究人员通过追踪细菌和古菌之间最早的分裂时期，重构了早期细胞的代谢化学反应网络[1]。该研究近期发表在《Science Advances》期刊上[1]。
研究发现，最后的通用祖先（LUCA）仅拥有完整代谢所需酶的约一半，其余部分由水热喷口环境中的金属催化[1]。这个完整代谢网络包含420个高度相连的化学反应[1]。研究表明，钯和磷酸盐等天然存在于水热喷口的物质可以替代ATP和酶进行代谢磷酸化反应[1]。
关键发现在于，细菌和古菌分别独立进化出了不同的酶来催化相同的代谢反应[1]。这一差异可能使它们能够逐渐独立于水热喷口环境的化学条件，最终转变为自由生活状态[1]。研究团队负责人William Martin表示："新数据只能得出一个结论。细菌和古菌分别独立地过渡到自由生活状态。只有自由生活细胞才是活的。让我们直言：我们看到的是一个遗传密码的起源，但生命的两个起源。"[1]这一事件发生在约40亿年前[1]。
An international research team has uncovered evidence suggesting that Earth's first free-living cells may have emerged independently on two separate occasions rather than once [1]. By tracing the earliest divergence between bacteria and archaea, researchers reconstructed the metabolic chemical reaction networks of primitive cells and discovered that bacteria and archaea likely evolved distinct enzymes independently to catalyze identical metabolic reactions [1]. This development may have enabled them to gradually become independent from the chemical conditions of hydrothermal vent environments [1].
The research, published in Science Advances, reveals that the Last Universal Common Ancestor (LUCA) possessed enzymes for only approximately half of the metabolic reactions required, with the remaining half catalyzed by metals present in the environment [1]. The complete metabolic network comprises 420 highly interconnected chemical reactions [1]. Scientists found that substances naturally occurring in hydrothermal vents, such as palladium and phosphate, could substitute for ATP and enzymes in metabolic phosphorylation reactions [1].
William Martin stated: "The new data can only lead to one conclusion. Bacteria and archaea independently made the transition to free-living status. Only free-living cells are alive. Let us be direct: we see the origin of one genetic code, but two origins of life" [1]. The research indicates these events occurred approximately four billion years ago [1].