School of Earth and Environmental Sciences, Seoul National University, Seoul, 08826, South Korea.
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA.
Nat Commun. 2019 Jan 9;10(1):44. doi: 10.1038/s41467-018-07878-4.
Sulfur isotope fractionation resulting from microbial sulfate reduction (MSR) provides some of the earliest evidence of life, and secular variations in fractionation values reflect changes in biogeochemical cycles. Here we determine the sulfur isotope effect of the enzyme adenosine phosphosulfate reductase (Apr), which is present in all known organisms conducting MSR and catalyzes the first reductive step in the pathway and reinterpret the sedimentary sulfur isotope record over geological time. Small fractionations may be attributed to low sulfate concentrations and/or high respiration rates, whereas fractionations greater than that of Apr require a low chemical potential at that metabolic step. Since Archean sediments lack fractionation exceeding the Apr value of 20‰, they are indicative of sulfate reducers having had access to ample electron donors to drive their metabolisms. Large fractionations in post-Archean sediments are congruent with a decline of favorable electron donors as aerobic and other high potential metabolic competitors evolved.
微生物硫酸盐还原（MSR）导致的硫同位素分馏为生命的起源提供了部分最早的证据，分馏值的长期变化反映了生物地球化学循环的变化。在这里，我们确定了在所有进行 MSR 的已知生物体中存在的腺苷磷酸硫酸还原酶（Apr）的硫同位素效应，该酶催化该途径的第一个还原步骤，并重新解释了地质时间内的沉积硫同位素记录。较小的分馏可能归因于低硫酸盐浓度和/或高呼吸速率，而大于 Apr 的分馏则需要在该代谢步骤中具有较低的化学势。由于太古代沉积物中缺乏超过 Apr 值 20‰的分馏，这表明硫酸盐还原菌能够获得足够的电子供体来驱动其新陈代谢。后太古代沉积物中的大分馏与作为好氧菌和其他高潜能代谢竞争者进化的有利电子供体的减少一致。
