scholarly journals Sulfur Isotope Effects of Dissimilatory Sulfite Reductase

2015 ◽  
Author(s):  
William D. Leavitt ◽  
Alexander S. Bradley ◽  
André A. Santos ◽  
Inês A.C. Pereira ◽  
David T. Johnston
Keyword(s):  
Sulfate Reduction ◽  
Isotope Effect ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Sulfite Reductase ◽  
Sulfate Reducers ◽  
Dissimilatory Sulfite Reductase

The precise interpretation of environmental sulfur isotope records requires a quantitative understanding of the biochemical controls on sulfur isotope fractionation by the principle isotope-fractionating process within the S cycle, microbial sulfate reduction (MSR). Here we provide the only direct observation of the major (34S/32S) and minor (33S/32S,36S/32S) sulfur isotope fractionations imparted by a central enzyme in the energy metabolism of sulfate reducers, dissimilatory sulfite reductase (DsrAB). Results from in vitro sulfite reduction experiments allow us to calculate the in vitro DsrAB isotope effect in34S/32S (hereafter,34ϵDsrAB) to be 15.3±2‰, 2σ. The accompanying minor isotope effect in33S, described as33λDsrAB, is calculated to be 0.5150±0.0012, 2σ. These observations facilitate a rigorous evaluation of the isotopic fractionation associated with the dissimilatory MSR pathway, as well as of the environmental variables that govern the overall magnitude of fractionation by natural communities of sulfate reducers. The isotope effect induced by DsrAB upon sulfite reduction is a factor of 0.3 to 0.6 times prior indirect estimates, which have ranged from 25 to 53‰ in34ϵDsrAB. The minor isotope fractionation observed from DsrAB is consistent with a kinetic or equilibrium effect. Our in vitro constraints on the magnitude of34ϵDsrABis similar to the median value of experimental observations compiled from all known published work, where34ϵr-p= 16.1‰ (r – pindicates reactant versus product, n = 648). This value closely matches those of MSR operating at high sulfate reduction rates in both laboratory chemostat experiments (34ϵSO4-H2S= 17.3±1.5‰) and in modern marine sediments (34ϵSO4-H2S= 17.3±3.8‰). Targeting the direct isotopic consequences of a specific enzymatic processes is a fundamental step toward a biochemical foundation for reinterpreting the biogeochemical and geobiological sulfur isotope records in modern and ancient environments.

scholarly journals Diversity of Sulfur Isotope Fractionations by Sulfate-Reducing Prokaryotes

2001 ◽  
Vol 67 (2) ◽  
pp. 888-894 ◽  
Author(s):  
Jan Detmers ◽  
Volker Brüchert ◽  
Kirsten S. Habicht ◽  
Jan Kuever
Keyword(s):  
Sulfate Reduction ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Reduction Rate ◽  
Sulfate Reduction Rate ◽  
Dissimilatory Sulfate Reduction ◽  
Systematic Effect ◽  
Sulfate Reducers ◽  
Sulfate Reducing ◽  
Sulfur Isotope Fractionation

ABSTRACT Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known sulfate reducers and cover a broad range of natural marine and freshwater habitats. Experimental conditions were designed to achieve optimum growth conditions with respect to electron donors, salinity, temperature, and pH. Under these optimized conditions, experimental fractionation factors ranged from 2.0 to 42.0‰. Salinity, incubation temperature, pH, and phylogeny had no systematic effect on the sulfur isotope fractionation. There was no correlation between isotope fractionation and sulfate reduction rate. The type of dissimilatory bisulfite reductase also had no effect on fractionation. Sulfate reducers that oxidized the carbon source completely to CO2 showed greater fractionations than sulfate reducers that released acetate as the final product of carbon oxidation. Different metabolic pathways and variable regulation of sulfate transport across the cell membrane all potentially affect isotope fractionation. Previous models that explained fractionation only in terms of sulfate reduction rates appear to be oversimplified. The species-specific physiology of each sulfate reducer thus needs to be taken into account to understand the regulation of sulfur isotope fractionation during dissimilatory sulfate reduction.

scholarly journals Effects of Iron and Nitrogen Limitation on Sulfur Isotope Fractionation during Microbial Sulfate Reduction

2012 ◽  
Vol 78 (23) ◽  
pp. 8368-8376 ◽  
Author(s):  
Min Sub Sim ◽  
Shuhei Ono ◽  
Tanja Bosak
Keyword(s):  
Nitrogen Fixation ◽  
Sulfate Reduction ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Reducing Power ◽  
Sulfate Reducing ◽  
Microbial Sulfate Reduction ◽  
Sulfur Isotope Fractionation ◽  
S Isotope

ABSTRACTSulfate-reducing microbes utilize sulfate as an electron acceptor and produce sulfide that is depleted in heavy isotopes of sulfur relative to sulfate. Thus, the distribution of sulfur isotopes in sediments can trace microbial sulfate reduction (MSR), and it also has the potential to reflect the physiology of sulfate-reducing microbes. This study investigates the relationship between the availability of iron and reduced nitrogen and the magnitude of S-isotope fractionation during MSR by a marine sulfate-reducing bacterium, DMSS-1, aDesulfovibriospecies, isolated from salt marsh in Cape Cod, MA. Submicromolar levels of iron increase sulfur isotope fractionation by about 50% relative to iron-replete cultures of DMSS-1. Iron-limited cultures also exhibit decreased cytochromec-to-total protein ratios and cell-specific sulfate reduction rates (csSRR), implying changes in the electron transport chain that couples carbon and sulfur metabolisms. When DMSS-1 fixes nitrogen in ammonium-deficient medium, it also produces larger fractionation, but it occurs at faster csSRRs than in the ammonium-replete control cultures. The energy and reducing power required for nitrogen fixation may be responsible for the reverse trend between S-isotope fractionation and csSRR in this case. Iron deficiency and nitrogen fixation by sulfate-reducing microbes may lead to the large observed S-isotope effects in some euxinic basins and various anoxic sediments.

scholarly journals Sulfur Isotope Effects of Dissimilatory Sulfite Reductase

2015 ◽  
Vol 6 ◽  
Author(s):  
William D. Leavitt ◽  
Alexander S. Bradley ◽  
André A. Santos ◽  
Inês A. C. Pereira ◽  
David T. Johnston
Keyword(s):  
Sulfur Isotope ◽  
Isotope Effects ◽  
Sulfite Reductase ◽  
Dissimilatory Sulfite Reductase

Stable isotope fractionation by Clostridium pasteurianum. 1.34S/32S: inverse isotope effects during SO42− and SO32− reduction

1975 ◽  
Vol 21 (3) ◽  
pp. 235-244 ◽  
Author(s):  
R. G. L. McCready ◽  
E. J. Laishley ◽  
H. R. Krouse
Keyword(s):  
Isotope Fractionation ◽  
Isotope Effects ◽  
Sulfite Reductase ◽  
Clostridium Pasteurianum ◽  
Stages Of Growth ◽  
Dissimilatory Sulfite Reductase ◽  
Stable Isotope Fractionation ◽  
High Concentrations ◽  
Late Stages ◽  
Isotopic Effects

During growth on minimal salts – sucrose media supplemented with various concentrations (10−4–10−2 M) of sodium sulfate, Clostridium pasteurianum grew at a normal rate and only evolved sulfide in late stages of growth on 10−2 M SO42−. The evolved sulfide was slightly enriched in 34S as compared to the medium sulfur. On the other hand, sulfide was evolved during growth on all concentrations of sulfite tested. Large normal and inverse isotopic effects were observed in the evolved sulfide during SO32− reductions. In contrast, the intracellular sulphur showed much smaller fractionations. The complexity of the isotopic patterns suggests that a dissimilatory sulfite reductase system may be induced by high concentrations of sulfite.

scholarly journals Oxygen isotope fractionation during N<sub>2</sub>O production by soil denitrification

2016 ◽  
Vol 13 (4) ◽  
pp. 1129-1144 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Jens Dyckmans ◽  
Jan Kaiser ◽  
Alina Marca ◽  
Jürgen Augustin ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Soil Water ◽  
Isotope Effect ◽  
Isotope Exchange ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
N2o Production ◽  
Oxygen Isotope Fractionation ◽  
Oxygen Isotope Exchange ◽  
Incubation Experiments

Abstract. The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by soil denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. In our soil incubation experiments Δ17O isotope tracing was applied for the first time to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found that N2O formation in static anoxic incubation experiments was typically associated with oxygen isotope exchange close to 100 % and a stable difference between the 18O ∕ 16O ratio of soil water and the N2O product of δ18O(N2O ∕ H2O)  =  (17.5 ± 1.2) ‰. However, flow-through experiments gave lower oxygen isotope exchange down to 56 % and a higher δ18O(N2O ∕ H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O ∕ H2O) showed a significant correlation (R2 = 0.70, p <  0.00001). We hypothesize that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of branching isotope effects at different steps in the reduction process. The results suggest that during denitrification, isotope exchange occurs prior to isotope branching and that this exchange is mostly associated with the enzymatic nitrite reduction mediated by NIR. For bacterial denitrification, the branching isotope effect can be surprisingly low, about (0.0 ± 0.9) ‰, in contrast to fungal denitrification where higher values of up to 30 ‰ have been reported previously. This suggests that δ18O might be used as a tracer for differentiation between bacterial and fungal denitrification, due to their different magnitudes of branching isotope effects.

The effect of pantothenate on sulfate metabolism and sulfur isotope fractionation by Saccharomyces cerevisiae

1979 ◽  
Vol 25 (10) ◽  
pp. 1139-1144 ◽  
Author(s):  
R. G. L. McCready ◽  
G. A. Din ◽  
H. R. Krouse
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Fatty Acids ◽  
Sulfate Reduction ◽  
Lipid Content ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Unsaturated Fatty Acids ◽  
Cellular Lipid ◽  
Sulfur Isotope Fractionation ◽  
Sulfate Metabolism

Growth of Saccharomyces cerevisiae in minimal salts – glucose – SO42− medium with varying concentrations of pantothenate (0–1000 μg/L) produced changes in the cellular lipid content and in the ratio of saturated to unsaturated fatty acids. Substantial differences in SO42−diffusion were also observed with changes in pantothenate concentration. During sulfate reduction, the δ34S value of the evolved sulfide varied with the pantothenate concentration ranging from −31‰ in the absence of pantothenate to 0‰ at 400−1000 μg/L pantothenate. The isotope selectivity is related to the effect of pantothenate concentration on cellular metabolism.

Why magnesium isotope fractionation is absent from basaltic melts under thermal gradients in natural settings

2019 ◽  
Vol 157 (7) ◽  
pp. 1144-1148
Author(s):  
Yingkui Xu ◽  
Dan Zhu ◽  
Xiongyao Li ◽  
Jianzhong Liu
Keyword(s):  
Isotope Fractionation ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Chemical Diffusion ◽  
Kinetic Isotope Effects ◽  
Thermal Gradients ◽  
Magnesium Isotopes ◽  
Magnesium Isotope ◽  
Natural Systems ◽  
Kinetic Isotope

AbstractLaboratory experiments have shown that thermal gradients in silicate melts can lead to isotopic fractionation; this is known as the Richter effect. However, it is perplexing that the Richter effect has not been documented in natural samples as thermal gradients commonly exist within natural igneous systems. To resolve this discrepancy, theoretical analysis and calculations were undertaken. We found that the Richter effect, commonly seen in experiments with wholly molten silicates, cannot be applied to natural systems because natural igneous samples are more likely to be formed out of partially molten magma and the presence of minerals adds complexity to the behaviour of the isotope. In this study, we consider two related diffusion-rate kinetic isotope effects that originate from chemical diffusion, which are absent from experiments with wholly molten samples. We performed detailed calculations for magnesium isotopes, and the results indicated that the Richter effect for magnesium isotopes is buffered by kinetic isotope effects and the total value of magnesium isotope fractionation can be zero or even undetectable. Our study provides a new understanding of isotopic behaviour during the processes of cooling and solidification in natural magmatic systems.

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