Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Science. 2011 Jul 1;333(6038):74-7. doi: 10.1126/science.1205103.
The composition of sulfur isotopes in sedimentary sulfides and sulfates traces the sulfur cycle throughout Earth's history. In particular, depletions of sulfur-34 ((34)S) in sulfide relative to sulfate exceeding 47 per mil (‰) often serve as a proxy for the disproportionation of intermediate sulfur species in addition to sulfate reduction. Here, we demonstrate that a pure, actively growing culture of a marine sulfate-reducing bacterium can deplete (34)S by up to 66‰ during sulfate reduction alone and in the absence of an extracellular oxidative sulfur cycle. Therefore, similar magnitudes of sulfur isotope fractionation in sedimentary rocks do not unambiguously record the presence of other sulfur-based metabolisms or the stepwise oxygenation of Earth's surface environment during the Proterozoic.
沉积硫化物和硫酸盐中硫同位素的组成追踪了地球历史上的硫循环。特别是，硫化物中硫-34((34)S)相对于硫酸盐的亏损超过 47 个千分比((34)S)通常是除硫酸盐还原以外的中间硫物种歧化的指标。在这里，我们证明了一种纯的、正在活跃生长的海洋硫酸盐还原细菌的培养物在没有细胞外氧化硫循环的情况下仅通过硫酸盐还原就可以将(34)S 耗尽高达 66‰。因此，在元古代，沉积岩中类似幅度的硫同位素分馏并不明确记录其他基于硫的代谢物的存在，也不记录地球表面环境的逐步氧化。
