title: Large sulfur isotope fractionation does not require disproportionation.
abstract: 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.
authors: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. mssim@mit.edu
authors: Min Sub
authors: MS
authors: Sim
authors: Tanja
authors: T
authors: Bosak
authors: Shuhei
authors: S
authors: Ono
mesh_terms: D003901:Desulfovibrio / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*; D019015:Geologic Sediments / Q000382:microbiology; D005947:Glucose / Q000378:metabolism; D010084:Oxidation-Reduction; D012623:Seawater / Q000737:chemistry / Q000382:microbiology; D013431:Sulfates / Q000378:metabolism*; D013440:Sulfides / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism; D013460:Sulfur Isotopes / Q000378:metabolism*; D013995:Time
chemical_list: D013431:Sulfates; D013440:Sulfides; D013460:Sulfur Isotopes; D013455:Sulfur; D005947:Glucose