34S enrichment as a signature of thiosulfate oxidation in the "Proteobacteria".

Kinetics of thiosulfate oxidation, product and intermediate formation, and 34S fractionation, were studied for the members of Alphaproteobacteria Paracoccus sp. SMMA5 and Mesorhizobium thiogangeticum SJTT, the Betaproteobacteria member Pusillimonas ginsengisoli SBO3, and the Acidithiobacillia member Thermithiobacillus sp. SMMA2, during chemolithoautotrophic growth in minimal salts media supplemented with 20 mM thiosulfate. The two Alphaproteobacteria oxidized thiosulfate directly to sulfate, progressively enriching the end-product with 34S; Δ34Sthiosulfate-sulfate values recorded at the end of the two processes (when no thiosulfate was oxidized any further) were -2.9‰ and -3.5‰, respectively. Pusillimonas ginsengisoli SBO3 and Thermithiobacillus sp. SMMA2, on the other hand, oxidized thiosulfate to sulfate via tetrathionate intermediate formation, with progressive 34S enrichment in the end-product sulfate throughout the incubation period; Δ34Sthiosulfate-sulfate, at the end of the two processes (when no further oxidation took place), reached -3.5‰ and -3.8‰, respectively. Based on similar 34S fractionation patterns recorded previously during thiosulfate oxidation by strains of Paracoccus pantotrophus, Advenella kashmirensis and Hydrogenovibrio crunogenus, it was concluded that progressive reverse fractionation, enriching the end-product sulfate with 34S, could be a characteristic signature of bacterial thiosulfate oxidation.

Effects of marine biofertilisation on Celtic bean carbon, nitrogen and sulphur isotopes: Implications for reconstructing past diet and farming practices.

RATIONALE: The application of fertilisers to crops can be monitored and assessed using stable isotope ratios. However, the application of marine biofertilisers (e.g., fish, macroalgae/seaweed) on crop stable isotope ratios has been rarely studied, despite widespread archaeological and historical evidence for the use of marine resources as a soil amendment. METHODS: A heritage variety of Celtic bean, similar in size and shape to archaeobotanical macrofossils of Vicia faba L., was grown in three 1 × 0.5 m outdoor plots under three soil conditions: natural soil (control); natural soil mixed with macroalgae (seaweed); and 15 cm of natural soil placed on a layer of fish carcasses (Atlantic cod). These experiments were performed over two growing seasons in the same plots. At the end of each growing season, the plants were sampled, measured and analysed for carbon, nitrogen and sulphur stable isotope ratios (δ13 C, δ15 N, δ34 S). RESULTS: The bean plants freely uptake the newly bioavailable nutrients (nitrogen and sulphur) and incorporate a marine isotopic ratio into all tissues. The bean δ15 N values ranged between 0.8‰ and 1.0‰ in the control experiment compared with 2‰ to 3‰ in the macroalgae crop and 8‰ to 17‰ in the cod fish experiment. Their δ34 S values ranged between 5‰ and 7‰ in the control compared with 15‰ to 16‰ in the macroalgae crop and 9‰ to 12‰ in the cod fish crop. The beans became more 13 C-depleted (δ13 C values: 1-1.5‰ lower) due to crop management practices. CONCLUSIONS: Humans and animals consuming plants grown with marine biofertilisers will incorporate a marine signature. Isotopic enrichment in nitrogen and sulphur using marine resources has significant implications when reconstructing diets and farming practices in archaeological populations.

The effect of temperature on sulfur and oxygen isotope fractionation by sulfate reducing bacteria (Desulfococcus multivorans).

Temperature influences microbiological growth and catabolic rates. Between 15 and 35 °C the growth rate and cell specific sulfate reduction rate of the sulfate reducing bacterium Desulfococcus multivorans increased with temperature. Sulfur isotope fractionation during sulfate reduction decreased with increasing temperature from 27.2 ‰ at 15 °C to 18.8 ‰ at 35 °C which is consistent with a decreasing reversibility of the metabolic pathway as the catabolic rate increases. Oxygen isotope fractionation, in contrast, decreased between 15 and 25 °C and then increased again between 25 and 35 °C, suggesting increasing reversibility in the first steps of the sulfate reducing pathway at higher temperatures. This points to a decoupling in the reversibility of sulfate reduction between the steps from the uptake of sulfate into the cell to the formation of sulfite, relative to the whole pathway from sulfate to sulfide. This observation is consistent with observations of increasing sulfur isotope fractionation when sulfate reducing bacteria are living near their upper temperature limit. The oxygen isotope decoupling may be a first signal of changing physiology as the bacteria cope with higher temperatures.

Tissue distribution of 35S-metabolically labeled neublastin (BG00010) in rats.

Neublastin (NBN) is a neurotrophic growth factor that promotes the survival and regenerative properties of nociceptive neurons and has been tested in clinical trials as a treatment for neuropathic pain in individuals with sciatica and painful lumbosacral radiculopathy. Like many low molecular weight heparin binding proteins, NBN is rapidly cleared from the blood following systemic administration. To explore ADME properties of NBN in rats, we used metabolically 35S-labeled NBN following IV and SC administration quantifying counts and intact protein in kidney, liver, brain, serum, and urine at 5 min, 8 h, 24 h and 48 h, and biodistribution in whole body carcasses by QWBA at 2, 8, 48, 96, and 168 h post dose. NBN is rapidly taken up by tissues mainly by liver and kidney and then degraded. Products of degradation are excreted in urine or recycled and utilized for resynthesis. The data we generated for NBN provides a first look at the complex clearance mechanisms for this protein and should aid in the design of ADME studies for other heparin binding proteins.

Plant sulphur metabolism is stimulated by photorespiration.

Intense efforts have been devoted to describe the biochemical pathway of plant sulphur (S) assimilation from sulphate. However, essential information on metabolic regulation of S assimilation is still lacking, such as possible interactions between S assimilation, photosynthesis and photorespiration. In particular, does S assimilation scale with photosynthesis thus ensuring sufficient S provision for amino acids synthesis? This lack of knowledge is problematic because optimization of photosynthesis is a common target of crop breeding and furthermore, photosynthesis is stimulated by the inexorable increase in atmospheric CO2. Here, we used high-resolution 33S and 13C tracing technology with NMR and LC-MS to access direct measurement of metabolic fluxes in S assimilation, when photosynthesis and photorespiration are varied via the gaseous composition of the atmosphere (CO2, O2). We show that S assimilation is stimulated by photorespiratory metabolism and therefore, large photosynthetic fluxes appear to be detrimental to plant cell sulphur nutrition.

Organic sulfur was integral to the Archean sulfur cycle.

The chemistry of the Early Earth is widely inferred from the elemental and isotopic compositions of sulfidic sedimentary rocks, which are presumed to have formed globally through the reduction of seawater sulfate or locally from hydrothermally supplied sulfide. Here we argue that, in the anoxic Archean oceans, pyrite could form in the absence of ambient sulfate from organic sulfur contained within living cells. Sulfides could be produced through mineralization of reduced sulfur compounds or reduction of organic-sourced sulfite. Reactive transport modeling suggests that, for sulfate concentrations up to tens of micromolar, organic sulfur would have supported 20 to 100% of sedimentary pyrite precipitation and up to 75% of microbial sulfur reduction. The results offer an alternative explanation for the low range of δ34S in Archean sulfides, and raise a possibility that sulfate scarcity delayed the evolution of dissimilatory sulfate reduction until the initial ocean oxygenation around 2.7 Ga.

Diversity decoupled from sulfur isotope fractionation in a sulfate-reducing microbial community.

The extent of fractionation of sulfur isotopes by sulfate-reducing microbes is dictated by genomic and environmental factors. A greater understanding of species-specific fractionations may better inform interpretation of sulfur isotopes preserved in the rock record. To examine whether gene diversity influences net isotopic fractionation in situ, we assessed environmental chemistry, sulfate reduction rates, diversity of putative sulfur-metabolizing organisms by 16S rRNA and dissimilatory sulfite reductase (dsrB) gene amplicon sequencing, and net fractionation of sulfur isotopes along a sediment transect of a hypersaline Arctic spring. In situ sulfate reduction rates yielded minimum cell-specific sulfate reduction rates < 0.3 × 10-15 moles cell-1  day-1 . Neither 16S rRNA nor dsrB diversity indices correlated with relatively constant (38‰-45‰) net isotope fractionation (ε34 Ssulfide-sulfate ). Measured ε34 S values could be reproduced in a mechanistic fractionation model if 1%-2% of the microbial community (10%-60% of Deltaproteobacteria) were engaged in sulfate respiration, indicating heterogeneous respiratory activity within sulfate-reducing populations. This model indicated enzymatic kinetic diversity of Apr was more likely to correlate with sulfur fractionation than DsrB. We propose that, above a threshold Shannon diversity value of 0.8 for dsrB, the influence of the specific composition of the microbial community responsible for generating an isotope signal is overprinted by the control exerted by environmental variables on microbial physiology.

Large sulfur isotope fractionation by bacterial sulfide oxidation.

A sulfide-oxidizing microorganism, Desulfurivibrio alkaliphilus (DA), generates a consistent enrichment of sulfur-34 (34 S) in the produced sulfate of +12.5 per mil or greater. This observation challenges the general consensus that the microbial oxidation of sulfide does not result in large 34 S enrichments and suggests that sedimentary sulfides and sulfates may be influenced by metabolic activity associated with sulfide oxidation. Since the DA-type sulfide oxidation pathway is ubiquitous in sediments, in the modern environment, and throughout Earth history, the enrichments and depletions in 34 S in sediments may be the combined result of three microbial metabolisms: microbial sulfate reduction, the disproportionation of external sulfur intermediates, and microbial sulfide oxidation.

Triple oxygen isotope evidence for limited mid-Proterozoic primary productivity.

The global biosphere is commonly assumed to have been less productive before the rise of complex eukaryotic ecosystems than it is today1. However, direct evidence for this assertion is lacking. Here we present triple oxygen isotope measurements (∆17O) from sedimentary sulfates from the Sibley basin (Ontario, Canada) dated to about 1.4 billion years ago, which provide evidence for a less productive biosphere in the middle of the Proterozoic eon. We report what are, to our knowledge, the most-negative ∆17O values (down to -0.88‰) observed in sulfates, except for those from the terminal Cryogenian period2. This observation demonstrates that the mid-Proterozoic atmosphere was distinct from what persisted over approximately the past 0.5 billion years, directly reflecting a unique interplay among the atmospheric partial pressures of CO2 and O2 and the photosynthetic O2 flux at this time3. Oxygenic gross primary productivity is stoichiometrically related to the photosynthetic O2 flux to the atmosphere. Under current estimates of mid-Proterozoic atmospheric partial pressure of CO2 (2-30 times that of pre-anthropogenic levels), our modelling indicates that gross primary productivity was between about 6% and 41% of pre-anthropogenic levels if atmospheric O2 was between 0.1-1% or 1-10% of pre-anthropogenic levels, respectively. When compared to estimates of Archaean4-6 and Phanerozoic primary production7, these model solutions show that an increasingly more productive biosphere accompanied the broad secular pattern of increasing atmospheric O2 over geologic time8.

Carbon, nitrogen and sulphur isotopic fractionation in captive juvenile hooded seal (Cystophora cristata): Application for diet analysis.

RATIONALE: Intrinsic biogeochemical markers, such as stable isotope ratios of carbon, nitrogen and sulphur, are increasingly used to trace the trophic ecology of marine top predators. However, insufficient knowledge of fractionation processes in tissues continues to hamper the use of these markers. METHODS: We performed a controlled feeding experiment with eight juvenile hooded seals (Cystophora cristata) that were held on a herring-based diet (Clupea harengus) for two years. Stable isotope ratios were measured via isotope ratio mass spectrometry in three of their tissues and related to values of these markers in their diet. RESULTS: Diet-tissue isotope enrichment (trophic enrichment factor, TEF) values between dietary herring and seal tissues for carbon (Δ13 C) were +0.7 ‰ for red blood cells, +1.9 ‰ for hair and +1.1 ‰ for muscle. The TEFs for nitrogen trophic (Δ15 N) were +3.3 ‰ for red blood cells, +3.6 ‰ for hair and +4.3 ‰ for muscle. For sulphur, the Δ34 S values were +1.1 ‰ for red blood cells, +1.0 ‰ for hair and +0.9 ‰ for muscle. CONCLUSIONS: These enrichment values were greater than those previously measured in adult seals. This increase may be related to the higher rate of protein synthesis and catabolism in growing animals. This study is the first report on sulphur isotope enrichment values for a marine mammal species.

The influence of sulfur and hair growth on stable isotope diet estimates for grizzly bears.

Stable isotope ratios of grizzly bear (Ursus arctos) guard hair collected from bears on the lower Stikine River, British Columbia (BC) were analyzed to: 1) test whether measuring δ34S values improved the precision of the salmon (Oncorhynchus spp.) diet fraction estimate relative to δ15N as is conventionally done, 2) investigate whether measuring δ34S values improves the separation of diet contributions of moose (Alces alces), marmot (Marmota caligata), and mountain goat (Oreamnos americanus) and, 3) examine the relationship between collection date and length of hair and stable isotope values. Variation in isotope signatures among hair samples from the same bear and year were not trivial. The addition of δ34S values to mixing models used to estimate diet fractions generated small improvement in the precision of salmon and terrestrial prey diet fractions. Although the δ34S value for salmon is precise and appears general among species and areas, sulfur ratios were strongly correlated with nitrogen ratios and therefore added little new information to the mixing model regarding the consumption of salmon. Mean δ34S values for the three terrestrial herbivores of interest were similar and imprecise, so these data also added little new information to the mixing model. The addition of sulfur data did confirm that at least some bears in this system ate marmots during summer and fall. We show that there are bears with short hair that assimilate >20% salmon in their diet and bears with longer hair that eat no salmon living within a few kilometers of one another in a coastal ecosystem. Grizzly bears are thought to re-grow hair between June and October however our analysis of sectioned hair suggested at least some hairs begin growing in July or August, not June and, that hair of wild bears may grow faster than observed in captive bears. Our hair samples may have been from the year of sampling or the previous year because samples were collected in summer when bears were growing new hair. The salmon diet fraction increased with later hair collection dates, as expected if samples were from the year of sampling because salmon began to arrive in mid-summer. Bears that ate salmon had shorter hair and δ15N and δ34S values declined with hair length, also suggesting some hair samples were grown the year of sampling. To be sure to capture an entire hair growth period, samples must be collected in late fall. Early spring samples are also likely to be from the previous year but the date when hair begins to grow appears to vary. Choosing the longest hair available should increase the chance the hair was grown during the previous year and, maximize the period for which diet is measured.

Evaluation of sulfur isotopic enrichment of urine metabolites for the differentiation of healthy and prostate cancer mice after the administration of 34S labelled yeast.

Sulfur isotopic enrichment of urine metabolites in healthy and prostate cancer mice using 34S enriched yeast and High Performance Liquid Chromatography coupled to Multicollector Inductively Coupled Plasma Mass Spectrometry (HPLC-MC-ICP-MS) has been evaluated. A 30 weeks experiment (since the eleventh to the fortieth week of life) was carried out collecting the urine of three healthy mice and three transgenic mice with prostate cancer during 24h after a single oral administration of a 34S enriched yeast slurry. The isotopic enrichment of different sulphur metabolites was monitored by coupling a C18 reverse phase HPLC column with a multicollector ICP-MS using a membrane desolvating system. Quantification of sulfur in the chromatographic peaks was carried out by post-column isotope dilution using a 33S enriched spike. Differences between the 34S enrichment in the urine metabolites of healthy and prostate cancer mice were found from the beginning of the disease. Both populations could be differentiated using a principal component analysis (PCA). Finally, 7 unknown mice were correctly classified in each population using a linear discriminant analysis.

15N-nitrate and 34S-sulfate isotopic fractionation reflects electron acceptor 'recycling' during hydrocarbon biodegradation.

The analysis of stable carbon isotopes for the assessment of contaminant fate in the aquifer is impeded in the case of petroleum hydrocarbons (TPH) by their chain length. Alternatively, the coupled nitrogen-sulfur-carbon cycles involved into TPH biodegradation under sulfate- and nitrate reducing conditions can be investigated using nitrogen (δ15N) and sulfur (δ34S) isotopic shifts in terminal electron acceptors (TEA) involved in anaerobic TPH oxidation. Biodegradation of a paraffin-rich crude oil was studied in anaerobic aquifer microcosms with nitrate (NIT), sulfate (SUL), nitrate plus sulfate (MIX) and nitrate under sulfate reduction suppression by molybdate (MOL) as TEA. After 8 months, TPH biodegradation was not different (around 33%) in experiments receiving only nitrate (NIT, MOL) versus under mixed TEA-conditions (MIX), despite higher biodiversity under mixed conditions (H'NIT and H'MOL≈5.9, H'MIX=8.0). Molybdate addition effected higher nitrate depletion, possibly by increasing the production of nitrate reductase. Additional sulfate depletion under mixed conditions suggested bioconversion of polar intermediates. Microcosms only receiving sulfate (SUL) showed no significant TEA and TPH decrease. A Rayleigh kinetic isotope enrichment model for isotopic 15N/14N and 34S/32S shifts in residual TEA gave apparent enrichment factors ɛN,NIT and ɛN,MOL values of -16.7 to -18.0‰ for nitrate as sole TEA and ɛN,MIX of -6.0‰ and ɛS,MIX of -4.1‰ under mixed electron accepting conditions. The low isotopic fractionation under mixed terminal electron accepting conditions was attributed to lithotrophic, sulfide-dependent denitrification by Thiobacillus species, while it was hypothesized that Desulfovibrio replenished the reduced sulfur pool via oxidation of polar hydrocarbon metabolites. Concurrently, organotrophic denitrification was performed by Pseudomonas species, with isotopic fractionation expressed by ɛN,MIX representing the superposition of both denitrification processes. This is, to our knowledge, the first characterization of sulfur and nitrogen isotopic shifts associated to concurrent organotrophic and lithotrophic denitrification in a hydrocarbon-contaminated environment, and offers the prospect of improved understanding of biogeochemical cycles including in situ hydrocarbon biotransformation.

Medical applications of Cu, Zn, and S isotope effects.

This review examines recent applications of stable copper, zinc and sulfur isotopes to medical cases and notably cancer. The distribution of the natural stable isotopes of a particular element among coexisting molecular species varies as a function of the bond strength, the ionic charge, and the coordination, and it also changes with kinetics. Ab initio calculations show that compounds in which a metal binds to oxygen- (sulfate, phosphate, lactate) and nitrogen-bearing moieties (histidine) favor heavy isotopes, whereas bonds with sulfur (cysteine, methionine) favor light isotopes. Oxidized cations (e.g., Cu(ii)) and low coordination numbers are expected to favor heavy isotopes relative to their reduced counterparts (Cu(i)) and high coordination numbers. Here we discuss the first observations of Cu, Zn, and S isotopic variations, three elements closely related along multiple biological pathways, with emphasis on serum samples of healthy volunteers and of cancer patients. It was found that heavy isotopes of Zn and to an even greater extent Cu are enriched in erythrocytes relative to serum, while the difference is small for sulfur. Isotopic variations related to age and sex are relatively small. The 65Cu/63Cu ratio in the serum of patients with colon, breast, and liver cancer is conspicuously low relative to healthy subjects. The characteristic time over which Cu isotopes may change with disease progression (a few weeks) is consistent with both the turnover time of the element and albumin half-life. A parallel effect on sulfur isotopes is detected in a few un-medicated patients. Copper in liver tumor tissue is isotopically heavy. In contrast, Zn in breast cancer tumors is isotopically lighter than in healthy breast tissue. 66Zn/64Zn is very similar in the serum of cancer patients and in controls. Possible reasons for Cu isotope variations may be related to the cytosolic storage of Cu lactate (Warburg effect), release of intracellular copper from cysteine clusters (metallothionein), or the hepatocellular and biosynthetic dysfunction of the liver. We suggest that Cu isotope metallomics will help evaluate the homeostasis of this element during patient treatment, notably by chelates and blockers of Cu trafficking, and understand the many biochemical pathways in which this element is essential.

Sulfur isotope fractionation during the evolutionary adaptation of a sulfate-reducing bacterium.

Dissimilatory sulfate reduction is a microbial catabolic pathway that preferentially processes less massive sulfur isotopes relative to their heavier counterparts. This sulfur isotope fractionation is recorded in ancient sedimentary rocks and generally is considered to reflect a phenotypic response to environmental variations rather than to evolutionary adaptation. Modern sulfate-reducing microorganisms isolated from similar environments can exhibit a wide range of sulfur isotope fractionations, suggesting that adaptive processes influence the sulfur isotope phenotype. To date, the relationship between evolutionary adaptation and isotopic phenotypes has not been explored. We addressed this by studying the covariation of fitness, sulfur isotope fractionation, and growth characteristics in Desulfovibrio vulgaris Hildenborough in a microbial evolution experiment. After 560 generations, the mean fitness of the evolved lineages relative to the starting isogenic population had increased by ∼ 17%. After 927 generations, the mean fitness relative to the initial ancestral population had increased by ∼ 20%. Growth rate in exponential phase increased during the course of the experiment, suggesting that this was a primary influence behind the fitness increases. Consistent changes were observed within different selection intervals between fractionation and fitness. Fitness changes were associated with changes in exponential growth rate but changes in fractionation were not. Instead, they appeared to be a response to changes in the parameters that govern growth rate: yield and cell-specific sulfate respiration rate. We hypothesize that cell-specific sulfate respiration rate, in particular, provides a bridge that allows physiological controls on fractionation to cross over to the adaptive realm.

Stable isotope turnover and half-life in animal tissues: a literature synthesis.

Stable isotopes of carbon, nitrogen, and sulfur are used as ecological tracers for a variety of applications, such as studies of animal migrations, energy sources, and food web pathways. Yet uncertainty relating to the time period integrated by isotopic measurement of animal tissues can confound the interpretation of isotopic data. There have been a large number of experimental isotopic diet shift studies aimed at quantifying animal tissue isotopic turnover rate λ (%·day(-1), often expressed as isotopic half-life, ln(2)/λ, days). Yet no studies have evaluated or summarized the many individual half-life estimates in an effort to both seek broad-scale patterns and characterize the degree of variability. Here, we collect previously published half-life estimates, examine how half-life is related to body size, and test for tissue- and taxa-varying allometric relationships. Half-life generally increases with animal body mass, and is longer in muscle and blood compared to plasma and internal organs. Half-life was longest in ecotherms, followed by mammals, and finally birds. For ectotherms, different taxa-tissue combinations had similar allometric slopes that generally matched predictions of metabolic theory. Half-life for ectotherms can be approximated as: ln (half-life) = 0.22*ln (body mass) + group-specific intercept; n = 261, p<0.0001, r2 = 0.63. For endothermic groups, relationships with body mass were weak and model slopes and intercepts were heterogeneous. While isotopic half-life can be approximated using simple allometric relationships for some taxa and tissue types, there is also a high degree of unexplained variation in our models. Our study highlights several strong and general patterns, though accurate prediction of isotopic half-life from readily available variables such as animal body mass remains elusive.

Large sulfur isotope fractionations associated with Neoarchean microbial sulfate reduction.

The minor extent of sulfur isotope fractionation preserved in many Neoarchean sedimentary successions suggests that sulfate-reducing microorganisms played an insignificant role in ancient marine environments, despite evidence that these organisms evolved much earlier. We present bulk, microdrilled, and ion probe sulfur isotope data from carbonate-associated pyrite in the ~2.5-billion-year-old Batatal Formation of Brazil, revealing large mass-dependent fractionations (approaching 50 per mil) associated with microbial sulfate reduction, as well as consistently negative Δ(33)S values (~ -2 per mil) indicative of atmospheric photochemical reactions. Persistent (33)S depletion through ~60 meters of shallow marine carbonate implies long-term stability of seawater sulfate abundance and isotope composition. In contrast, a negative Δ(33)S excursion in lower Batatal strata indicates a response time of ~40,000 to 150,000 years, suggesting Neoarchean sulfate concentrations between ~1 and 10 µM.

Intracellular metabolite levels shape sulfur isotope fractionation during microbial sulfate respiration.

We present a quantitative model for sulfur isotope fractionation accompanying bacterial and archaeal dissimilatory sulfate respiration. By incorporating independently available biochemical data, the model can reproduce a large number of recent experimental fractionation measurements with only three free parameters: (i) the sulfur isotope selectivity of sulfate uptake into the cytoplasm, (ii) the ratio of reduced to oxidized electron carriers supporting the respiration pathway, and (iii) the ratio of in vitro to in vivo levels of respiratory enzyme activity. Fractionation is influenced by all steps in the dissimilatory pathway, which means that environmental sulfate and sulfide levels control sulfur isotope fractionation through the proximate influence of intracellular metabolites. Although sulfur isotope fractionation is a phenotypic trait that appears to be strain specific, we show that it converges on near-thermodynamic behavior, even at micromolar sulfate levels, as long as intracellular sulfate reduction rates are low enough (<<1 fmol H2S⋅cell(-1)⋅d(-1)).

A preliminary study on sulfate reduction bacteria behaviors in groundwater by sulfur and carbon isotopes: a case study in Jiaozuo City, China.

Inorganic pollutants in groundwater, such as sulfate and nitrate, have been a serious problem in China for decades. These pollutants are difficult to be removed because of their high solubility and ease of transport in subsurface environment. It had been found that microorganism could be one of the most feasible methods for inorganic pollutant elimination. During the process of degradation, some microorganisms can utilize sulfur and nitrogen in sulfate and nitrate forms, respectively, as energy sources. Meanwhile, significant variations of sulfur stable isotope ratios happened. Therefore sulfur isotope can be used as a good indicator for pollutant degradation and microbial activities. Shallow groundwater (SGW), deep groundwater (DGW), and surface water (SFW) were investigated in alluvial plain in Jiaozuo City, China. The results of hydrochemical analysis indicated that K(+), Na(+), and HCO3(-) were dominant ions in DGW, Mg(2+) and HCO3(-) were dominant ions in SGW, and Ca(2+) and HCO3 (-) were dominant in SFW except for LR sample. A wide variation of δ (34)SSO4 values ranging from + 7.3 to +23.6‰ had been observed for all water samples, with a mean value of +20.7, +12.6 and +10.0‰ for DGW, SGW, and SFW respectively. At the same time, δ(13)C values of dissolved inorganic carbon (DIC) ranged from -12.4 to -5.7‰, with a mean value of -7.5, -9.0, and -9.6‰ for DGW, SGW, and SFW, respectively. The microbial degradation processes resulted in significant sulfur isotope fractionations in DGW. Organic carbon was utilized by bacteria and transferred into inorganic carbon, leading to negative fractionation of carbon isotopes. Thus the variations in stable isotope ratios of sulfur and carbon in groundwater can be used as good indicators for understanding of the relationship between bacteria behaviors and sulfate degradation.