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

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.

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 Coupling of Functional Gene Diversity and Geochemical Data from Environmental Samples

2004 ◽  
Vol 70 (11) ◽  
pp. 6525-6534 ◽  
Author(s):  
A. V. Palumbo ◽  
J. C. Schryver ◽  
M. W. Fields ◽  
C. E. Bagwell ◽  
J.-Z. Zhou ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Small Sample ◽  
Geochemical Data ◽  
Sulfite Reductase ◽  
Model Parameters ◽  
Generalization Error ◽  
Sample Sizes ◽  
Dissimilatory Sulfite Reductase ◽  
Small Sample Sizes ◽  
Error Weight

ABSTRACT Genomic techniques commonly used for assessing distributions of microorganisms in the environment often produce small sample sizes. We investigated artificial neural networks for analyzing the distributions of nitrite reductase genes (nirS and nirK) and two sets of dissimilatory sulfite reductase genes (dsrAB 1 and dsrAB 2) in small sample sets. Data reduction (to reduce the number of input parameters), cross-validation (to measure the generalization error), weight decay (to adjust model parameters to reduce generalization error), and importance analysis (to determine which variables had the most influence) were useful in developing and interpreting neural network models that could be used to infer relationships between geochemistry and gene distributions. A robust relationship was observed between geochemistry and the frequencies of genes that were not closely related to known dissimilatory sulfite reductase genes (dsrAB 2). Uranium and sulfate appeared to be the most related to distribution of two groups of these unusual dsrAB-related genes. For the other three groups, the distributions appeared to be related to pH, nickel, nonpurgeable organic carbon, and total organic carbon. The models relating the geochemical parameters to the distributions of the nirS, nirK, and dsrAB 1 genes did not generalize as well as the models for dsrAB 2. The data also illustrate the danger (generating a model that has a high generalization error) of not using a validation approach in evaluating the meaningfulness of the fit of linear or nonlinear models to such small sample sizes.

Sulfur isotope effects in the hydrogen ion decomposition of polythionates

1967 ◽  
Vol 45 (2) ◽  
pp. 181-187 ◽  
Author(s):  
U. Agarwala ◽  
C. E. Rees ◽  
H. G. Thode
Keyword(s):  
Sulfur Isotope ◽  
Isotope Effects ◽  
Experimental Results ◽  
Hydrogen Ion ◽  
Rate Controlling Step ◽  
Sulfur Bond

The sulfur isotope effects in the decomposition of tri-, tetra-, and penta-thionate have been studied. There are three distinct intermolecular and three distinct intramolecular isotope effects. The experimental results show that the decomposition of these polythionates may be described in terms of a model where the rate-controlling step is the cleavage of a sulfur–sulfur bond, and that the appropriate cleavage forms are (S2O32−) (SO3), (S3O3) (SO32−), and (S4O3) (SO32−) for tri-, tetra-, and penta-thionate, respectively.

Stable isotope fractionation by Clostridium pasteurianum. 4. Sulfur isotope fractionation during enzymatic S3O62−, S2O32−, and SO32− reductions

1981 ◽  
Vol 27 (8) ◽  
pp. 824-834
Author(s):  
G. I. Harrison ◽  
E. J. Laishley ◽  
H. R. Krouse
Keyword(s):  
Stable Isotope ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Growth Conditions ◽  
Enzyme Concentration ◽  
Clostridium Pasteurianum ◽  
Relative Reduction ◽  
Stable Isotope Fractionation ◽  
Sulfur Isotope Fractionation

Cell-free extracts from Clostridium pasteurianum grown on SO32− utilize H2 to reduce S3O62−, S2O32−, and SO32− to H2S at a much faster rate than extracts from SO42−-grown cells. This further supports the concept of an inducible dissimilatory type SO32− reductive pathway in this organism. 35S dilution experiments further support the concept that S3O62− and S2O32− are pathway intermediates. The inducible SO32− reductase is ferredoxin linked and the kinetics of the reduction and the sulfur isotope fractionation of the product can be altered by altering the growth conditions. The attending sulfur isotope fractionations are similar to those observed during the chemical decomposition of these compounds. In the case of S2O32−, 35S labelling experiments verified the conclusions derived from the stable isotope fractionation data concerning the relative reduction rates of the sulfane and sulfonate sulfurs. The reduction rates were also affected by enzyme concentration. The integrity of the whole cell is a necessary requirement for the large inverse isotope effects previously reported.

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