Combined 34S, 33S and 18O isotope fractionations record different intracellular steps of microbial sulfate reduction

Oxygen isotope effects during microbial sulfate reduction: applications to sediment cell abundances

“…There exists a rich literature of sulfate oxygen isotope data from environmental settings ( [26] and references within), and pure culture experiments ( [19,24,25,28,17]), and a framework for how MSR drives sulfate oxygen isotopic signatures is emerging. However, much is still lacking with respect to our knowledge of intracellular conditions, and the isotopic consequences therein.…”

“…Porewater with low relative sulfate reduction rates exhibiting strong non-linearity (dark blue circles), whereas settings capturing elevated sulfate reduction rates show a linear trend (green circles). b Isotopic offset between porewater sulfates and ambient water compositions and sulfur isotopic compositions (expressed relative to the international standard, VCDT, expressed in units of per mil, ‰) during recent microbial sulfate reduction batch experiments [17,19,24,25,28]). oxygen-free N 2 :CO 2 (90:10) gas, maintaining anaerobic conditions.…”

“…This approach is long-standing concerning the sulfate sulfur isotopic composition [11][12][13][14][15], but less explored in the case of sulfate oxygen isotope ratios [16][17][18]. Broadly, the oxygen isotopic composition of sulfate is interpreted to reflect sulfate consumption via MSR and sulfate regeneration through microbial sulfide oxidation and sulfur disproportionation [16,[18][19][20][21][22]. This is depicted in detail in Fig.…”

“…The figure shows the sulfate oxygen isotopic composition in porewaters (Panel a) and pure cultures (Panel b) undergoing active MSR, and highlights the role of sulfate reduction rates in the development of this oxygen isotopic signature. Recently, this interpretation has been extended to include the biochemistry of MSR and its specific role in modern marine environments, highlighting the potential of sulfate oxygen isotopic compositions to refine paleoenvironmental reconstructions [19,21,[23][24][25][26][27][28][29][30]. Implicit in this new approach is isolating the reductive and oxidative fluxes within the MSR biochemistry.…”

“…We aim to quantitatively link the MSR biogeochemistry and its oxygen isotope effect. Mathematical frameworks have been developed to establish quantitative links between cell-specific parameters (i.e., rate [17,19,20,24]) and the temperature and pH-sensitive [31] equilibrium oxygen isotope exchange between intracellular sulfur species and ambient water [29,[32][33][34][35]. This equilibrium oxygen isotope effect places a critical oxygen isotope equilibration step within the dissimilatory sulfate reduction pathway ( Fig.…”