Microbial oxidation of elemental sulphur in brown soil

Plant and Soil - Brown soil formed from loamy clay was examined for its ability to produce sulphate from added elemental suphur. At higher rates of sulphur applications the pH of a slightly acid...     

Effects of organic matter on sulphur oxidation in soil and influence of sulphur oxidation on soil nitrification

Summary The effects of wheat straw and pressed sugar beet pulp on sulphur oxidation were determined in a loam soil amended with 1% (w/w) elemental sulphur. Wheat straw stimulated the oxidation of elemental sulphur over the first 2 to 3 weeks of the incubation period, resulting in an increase in LiCl-extractable sulphate. After 4 to 7 weeks incubation however, the only significant increase in soil sulphate followed the 1% straw addition, while at week 7 sulphate concentrations in the 0.25% and 5.0% straw amended soils were lower than the control. Pressed sugar beet pulp (1% w/w) initially stimulated the oxidation of elemental sulphur in the soil, but by weeks 3 to 7 of the incubation period rates of oxidation in pulp-amended soils were lower than the control. Towards the end of the incubation period however, sulphate concentrations in the amended soils exceeded the control values, significantly so by week 11. The concentration of thiosulphate and tetrathionate also increased in soils receiving sugar beet pulp. Nitrification was inhibited in soils in which sulphur oxidation was actively occurring. Although possible alternatives are mentioned, such inhibition appears to result from a decrease in soil pH brought about by the oxidation of elemental sulphur to sulphuric acid.     

Transformations and plant uptake of urine-sulphate in urine-affected areas of pasture soil

The fate of sheep urine sulphate in the soil and its plant uptake was monitored using ³⁵S-labelled sulphate-S in undisturbed pasture microplots in two glasshouse experiments. The extent of macropore flow of simulated urine immediately following a sheep urination was also investigated at 5 pasture sites in the field. Immediately following urination to pasture microplots in the glasshouse, the amounts of urinederived ³⁵S recovered in the 0–2.5, 2.5–7.5, 7.5–15 and 15–30 cm soil layers were 38, 28, 18 and 9%, respectively. In the field study on 5 contrasting soils, a similar pattern was found with 55–70, 20–35 and 13–20% of simulated urine being recovered in the 0–5, 5–10 and 10–15 cm soil layers, respectively. There was insignificant loss below 15 cm. If urine had moved via simple displacement in these soils the wetting front would have reached only 2.0–2.5 cm in depth suggesting that significant downward movement of urine via macropore flow occurs after urination. In a 15-day period following urine application to a pasture soil there was a rapid rate of incorporation of ³⁵S into organic forms, while between 15 and 64 days the rate of incorporation declined. After 7 days, 27% of added ³⁵S had been incorporated into organic forms with 19% being C-bonded S and 8% Hl-reducible S. This rapid incorporation was attributed to the large and active microbial biomass present in the rhizosphere. Since urine application depressed pasture growth, due to ‘urine burn’, less than 10% of applied ³⁵S was absorbed by pasture plants over a 64-day period. A second experiment using microplots of contrasting soil types, confirmed that the majority of the ³⁵S incorporated into the organic form was present as C-bonded S. Results showed that of the ³⁵S remaining in the 0–2.5 cm layer 35 days after application, 20–40% was present as sulphate, 10–20% as Hl-reducible S and 50–60% as C-bonded S. Plant uptake of S accounted for only 7–12% of applied ³⁵S over the 35-day period.     

Oxidation of elemental sulfur by bacteria and fungi in soil

Laboratory experiments were used to determine the effects of antibiotics, organic C and CaCO3 amendments of sterile reinoculated soil on S0 oxidation by bacteria and fungi. The rate of S0 oxidation in soil with nystatin added was higher than in soil amended with penicillin + streptomycin. This tells us that bacteria were more efficient than fungi in the S0 oxidation process. It was demonstrated that neutrophilic chemolithotrophs were more efficient in this process than heterotrophs. Glucose introduced to the soil had a negative effect and CaCO3 had a positive effect on S0 oxidation. In soil enriched with glucose the number of chemolithotrophs was very low in comparison with extremely numerous heterotrophic bacteria and fungi. It suggests that the role of heterotrophs in S0 oxidation could be important in habitats rich in organic C, e.g. rhizosphere. In soil containing S0, qualitative changes of fungal communities to genera with higher S0 oxidation ability was also noted. In the presented paper, after comparison of the own results with the data of others concerning the natural soils, the role of various microbial groups in S0 oxidation process in soils is discussed.     

Extractable sulphate and organic sulphur in soils and their availability to plants

Ten soils collected from the major arable areas in Britain were used to assess the availability of soil sulphur (S) to spring wheat in a pot experiment. Soils were extracted with various reagents and the extractable inorganic SO₄-S and total soluble S(SO₄-S plus a fraction of organic S) were determined using ion chromatography (IC) or inductively-coupled plasma atomic emission spectrometry (ICP-AES), respectively. Water, 0.016 M KH₂PO₄, 0.01 M CaCl₂ and 0.01 M Ca(H₂PO₄)₂ extracted similar amounts of SO₄-S, as measured by IC, which were consistently smaller than the total extractable S as measured by ICP-AES. The amounts of organic S extracted varied widely between different extractants, with 0.5 M NaHCO₃ (pH 8.5) giving the largest amounts and 0.01 M CaCl₂ the least. Organic S accounted for approximately 30–60% of total S extracted with 0.016 M KH₂PO₄ and the organic C:S ratios in this extract varied typically between 50 and 70. The concentrations of this S fraction decreased in all soils without added S after two months growth of spring wheat, indicating a release of organic S through mineralisation. All methods tested except 0.5 M NaHCO₃-ICP-AES produced satisfactory results in the regression with plant dry matter response and S uptake in the pot experiment. In general, 0.016 M KH₂PO₄ appeared to be the best extractant and this extraction followed by ICP-AES determination was considered to be a good method to standardise on.     

Mobilization of sulphur in soybean cotyledons during germination

Soybean seeds ( Glycine max L. cv , Stephens) contain a large amount of sulphur (ca 40 μ mol seed⁻¹), mostly in the insoluble fraction in the cotyledons. During germination in nutrient solution lacking sulphur the amount of insoluble sulphur decreases to very low levels. This is accompanied by a transitory increase in the pool of soluble sulphur which then declines. All of the sulphur lost from the cotyledons is quantitatively recovered in the seedling. In the short term, the root and the stem are the most important sinks for sulphur from the cotyledons but as growth proceeds the shoot becomes the dominant sink for remobilized sulphur. Within the shoot most of the sulphur is recovered in leaves L1 and L2. The growth of L3 and, to a lesser extent, L2, was retarded due to sulphur insufficiency. The cotyledons of plants treated with 20 μ M sulphate also exhibited mobilization of sulphur from the insoluble fraction except that the maximum rate of loss of sulphur occurred somewhat later. Plants grown with sulphate exhibited a net gain of sulphur and did not exhibit sulphur insufficiency. In these plants, endogenous sulphur from the cotyledons was directed into L1–L3 and this sulphur remained within these leaves for the duration of the experiment. The delivery of exogenous sulphur (supplied as [³⁵S]sulphate via the roots) to the leaves increased with leaf number. In leaves L1–L3, the level of exogenous sulphur in any one leaf declined with time, indicating that this sulphur was remobilized and did not mix with the sulphur derived from the cotyledons. It was concluded that the cotyledons are an important source of sulphur to support early plant growth and development of soybean.     

Combustion losses of sulphur from conifer foliage: Implications of chemical form and soil nitrogen status

The proportion of total sulphur lost during combustion (600 °C) of Douglas-fir (Pseudotsuga menziesii) foliage is reduced from> 90% to 65–70% as the SO₄-S concentration increases from 10% to 45–50% of the total S content. Foliar SO₄-S content is decreased by improvement of plant nitrogen status, suggesting that alterations to soil N availability may influence S transfer to the atmosphere during biomass burning.     

Sulphur oxidation by a Streptomyces sp. growing in a carbon-deficient medium and autoclaved soil

Streptomyces colonies, apparently all of the same species, were isolated from a range of soils using a polysulphide medium lacking an organic carbon source. Growth on this medium, and clearing of the otherwise white, opaque overlay, suggested that the organisms were capable of growing autotrophically. However, investigation of one of these isolates showed that it was unable to fix ¹⁴CO₂ and did not possess the enzyme ribulose bisphosphate carboxylase, showing that it was incapable of autotrophic growth. The isolate oxidized elemental sulphur, thiosulphate and tetrathionate to sulphate in vitro in carbon-deficient medium, and also oxidized elemental sulphur to sulphate when inoculated into autoclaved soil supplemented with sulphur. It also oxidized polysulphide when growing on Czapek Dox and plate count agars. The isolate can therefore grow heterotrophically in both carbon-rich media and in media lacking organic carbon — presumably by scavenging organic carbon from the laboratory atmosphere. The possible role of these organisms in sulphur oxidation in soils is commented upon.     

Effect of nitrogen nutrition on the export of sulphur from leaves in soybean

Soybean plants were grown in complete solution for 33 days and then transferred to medium containing inadequate sulphur (5 t M) and nitrogen at 15, 7.5, 2 or 0.25 mt M. In mature leaves (L1 and L2), and leaves that were 70% expanded at day 33 (L3), the net loss of sulphur over the ensuing 25 days was inversely related to the level of nitrogen nutrition. Leaf 5, which formed during the study period, exhibited complementary characteristics; the increase in the sulphur content was inversely related to the level of nitrogen nutrition even though low nitrogen nutrition supported less growth. L4, which was 31% expanded at day 33, exhibited intermediate characteristics. 35S-Labelled sulphate was supplied to all of the plants for 48 h at day 31 and was distributed principally to L3 at day 33. During early development, L5 became heavily labelled but, at low nitrogen nutrition, the massive import of total sulphur into L5 during the late stages of development was not accompanied by a commensurate increase in 35S-label, indicating that redistribution of soluble sulphur from mature leaves was not involved. The loss of sulphur from mature leaves was parallelled by similar changes in nitrogen at all levels of nitrogen nutrition. Collectively, the data suggest that a common mechanism, presumably proteolysis, is involved in the export of sulphur and nitrogen from mature leaves and that this process is inhibited at high levels of nitrogen nutrition, even under conditions of sulphur deficiency.     

Stable sulphur isotopes in plants: a review

The determination of the natural abundances of stable isotopes has become a useful method by which to study the transformations of elements in biological and ecological studies as well as to investigate the mechanisms of chemical reactions. Unlike carbon and nitrogen isotopes, however, stable sulphur isotopes are used infrequently, and their potential as tracers in biochemical and physiological studies are only beginning to be realized. This review provides an overview of research involving stable sulphur isotopes in studies of plant metabolism and pollution. Topics discussed include the mechanisms and accompanying isotopic fractionations involved during the uptake and assimilation of inorganic sulphur compounds by plants, the utility of plants as bioindicators of environmental sulphur pollution, and the emission of isotopically light H₂S by plants in response to high concentations of sulphur. Future advances in the field are proposed.     

Biological sulphide oxidation in a fed-batch reactor

This study shows that, in a sulphide-oxidizing bioreactor with a mixed culture of Thiobacilli, the formation of sulphur and sulphate as end-products from the oxidation of sulphide can be controiledinstantaneously and reversibiy by the amount of oxygen supplied. It was found that at sulphide loading rates of up to 2.33 mmol7/L . h, both products can be formed already at oxygen concentrations below 0.1 mg/L. Because the microorganisms tend to form sulphate rather than forming sulphur, the oxygen concentration is not appropriate to optimize the sulphur production. Within less than 2 h, the system can be switched reversibly from sulphur to sulphate formation by adjusting the oxygen flow. This is below the minimum doubling time (2.85 h) of, e.g., Thiobacillus neapolitanus and Thiobacillus 0,(18) which indicates that one metabolic type of organism can probably perform both reactions. Under highly oxygen-limited circumstances, that is, at an oxygen/sulphide consumption ratio below 0.7 mol . h(-1) mol . h(-1) thiosulphate is abundantly formed. Because the chemical sulphide oxidation results mainly in the formation of thiosulphate, it is concluded that, under these circumstances, the biological oxidation capacity of the system is lower than the chemical oxidation capacity. The oxidation rate of the chemical sulphide oxidation can be described by a first-order process (k =-0.87 h(-1)).(c) 1995 John Wiley & Sons, Inc.     

Calcium content of liming material and its effect on sulphur release in a coniferous forest soil

Soil columns with O + A (Experiment I) or Ohorizons (Experiment II) from a Haplic Podsol wereincubated at 15 °C for 368 and 29 + 106 days,respectively. Three types of liming material differingin Ca²⁺ content, i.e. calcium carbonate(CaCO₃), dolomite (CaMg(CO₃)₂) andmagnesium carbonate (MgCO₃), were mixed into theO horizons in equimolar amounts corresponding to 6000kg of CaCO₃ per ha. In the limed treatments ofExperiment I, the leaching of dissolved organic carbon(DOC) and the net sulphur mineralization (estimated asaccumulated SO₄^2– leaching corrected forchanges in the soil pools of adsorbed and waterextractable SO₄^2–) increased with decreasingCa²⁺ content of the lime and increasing degree oflime dissolution. In relation to the controltreatment, only the MgCO₃ treatment resulted ina significantly higher net sulphur mineralization. InExperiment I the net sulphur mineralization was 4.06,1.68, 0.57, and 2.14 mg S in the MgCO₃,CaMg(CO₃)₂, CaCO₃ and control treatment,respectively. The accumulated SO₄^2– leachingin Experiment II during the first 29 days was 1.70,0.74 and 0.48 mg S in the MgCO₃,CaMg(CO₃)₂ and control treatment,respectively. In the two experiments there wereconsistently significant positive correlations betweenleached amounts of SO₄^2– and DOC. It wasconcluded that net sulphur mineralization was stronglyconnected to the solubilization of the organic matter(DOC formation) and that pH and/or Ca²⁺ ionsaffected the net sulphur mineralization through theireffects on organic matter solubility.     

Oxidation of reduced sulphur compounds by intact cells of Thiobacillus acidophilus

Oxidation of reduced sulphur compounds by Thiobacillus acidophilus was studied with cell suspensions from heterotrophic and mixotrophic chemostat cultures. Maximum substrate-dependent oxygen uptake rates and affinities observed with cell suspensions from mixotrophic cultures were higher than with heterotrophically grown cells. ph Optima for oxidation of sulphur compounds fell within the pH range for growth (pH 2–5), except for sulphite oxidation (optimum at pH 5.5). During oxidation of sulphide by cell suspensions, intermediary sulphur was formed. Tetrathionate was formed as an intermediate during aerobic incubation with thiosulphate and trithionate. Whether or not sulphite is an inter-mediate during sulphur compound oxidation by T. acidophilus remains unclear. Experiments with anaerobic cell suspensions of T. acidophilus revealed that trithionate metabolism was initiated by a hydrolytic cleavage yielding thiosulphate and sulphate. A hydrolytic cleavage was also implicated in the metabolism of tetrathionate. After anaerobic incubation of T. acidophilus with tetrathionate, the substrate was completely converted to equimolar amounts of thiosulphate, sulphur and sulphate. Sulphide- and sulphite oxidation were partly inhibited by the protonophore uncouplers 2,4-dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) and by the sulfhydryl-binding agent N-ethylmaleimide (NEM). Oxidation of elemental sulphur was completely inhibited by these compounds. Oxidation of thiosulphate, tetrathionate and trithionate was only slightly affected. The possible localization of the different enzyme systems involved in sulphur compound oxidation by T. acidophilus is discussed.     

Thiobacillus strain Q,a chemolithoheterotrophic sulphur bacterium

The physiological properties of an organism isolated from a selective chemostat enrichment using acetate and thiosulphate as the limiting substrates, provisionally called Thiobacillus Q, were investigated. Although the organism made up 85% of the community in the enrichment culture, its expected chemolithotrophic nature was not apparent in batch experiments. The growth yield was not enhanced by the addition of thiosulphate to an acetate containing mineral medium, even though up to 50% of the thiosulphate was oxidized. Under acetate limitation in the chemostat, there was a linear increase in yield with thiosulphate addition up to a concentration of 7 mM. Higher thiosulphate concentrations resulted in loss of thiosulphate oxidizing capacity and a decrease in the biomass to the level obtained with acetate alone. This loss may be due to the presence of inhibitory (50–100 M) levels of sulphite which is probably produced as an intermediate of the biological thiosulphate oxidation. Experiments with sulphide showed that Thiobacillus Q could also use it as an additional energy source. The complete lack of autotrophic growth, both in batch and chemostat experiments, together with the absence of even very low amounts of the key enzymes of the Calvin cycle demonstrated that this organism is a typical chemolithoheterotroph. Although this organism has provisionally been placed in the genus Thiobacillus, standard taxonomic procedures showed a close relationship with Pseudomonas alcaligenes. This study stresses the importance of quantitative chemostat studies in establishing the role of inorganic oxidations in energy metabolism and in the understanding of the role of heterotrophic sulphur oxidation in natural environments.     

The content of total sulphur and sulphur forms in birch (Betula pendula Roth) leaves in the air-polluted Krusne hory mountains

In leaves of birch (Betula pendula Roth), changes in the content of total sulphur and its inorganic and organic forms were determined in relation to the decreasing air-pollution load (SO₂) in the air-polluted Krusne hory mountains and the Decin sandstone highlands in 1995, 1998, 2001 and 2004. Results have shown that birch is able to use considerable amounts of sulphur taken through leaves from air-pollution load. Birch responds fast to changes in air-pollution load by fall in the content of total and inorganic forms of sulphur in leaves.     

Availability of different forms of sulphur fertilisers to wheat and oilseed rape

A pot experiment was conducted to compare the availability and efficiency of three sulphur (S) fertilisers to wheat in the first year and oilseed rape in the second year, using six agricultural soils. Four treatments were applied in the initial year: control (no S), two forms of elemental S (either micronised S° particles or a bentonite + S° mixture) and a sulphate fertiliser (ammonium sulphate). In the first year, the micronised S° was as effective as the sulphate fertiliser, both producing similar increases of wheat grain yield (on average 36%) and S uptake (on average 164%) over the control. In contrast, responses to the bentonite + S° form were minimal, indicating a limited S supply. In the second year the control treatment failed to produce seeds in most soils, whereas the micronised S° and sulphate treatments increased seed yields of oilseed rape to an average of 13.4 and 12.9 g pot^-1, respectively. The performance of the bentonite + S° varied between soils: two soils produced yields similar to those of the other S fertilisers, while the remaining soils had low yields. To test whether the poor performance of the bentonite clay + S° fertiliser was due to the lack of exposure of the prills to physical weathering in the glasshouse, the effect of freeze-thaw action on the fertilisers performance was assessed in a separate pot experiment. The responses in wheat yield and S uptake showed that freeze-thaw did not enhance the physical disruption of the prills or fertiliser effectiveness. These results suggest that the release of available S from the bentonite + S° mixture was too slow to meet the requirement of wheat and oilseed rape. This revised version was published online in June 2006 with corrections to the Cover Date.     

Plant uptake of sulphur as related to changes in the HI-reducible and total sulphur fractions in soil

Although considerable progress has been made in relating extractable soil S to plant S availability, most of these studies determined the extractable soil S at the beginning of the experiment to use as an index of soil S status. This bears little or no relationship to the S taken up by plants during the entire growing season. The present study investigates the changes in extractable soil S with time and relates these to changes in plant S uptake. Six soils with different long-term fertiliser histories (0, 21, 42 kg of S as superphosphate ha^–1 applied since 1952) and animal camping treatments (camp and non-camp) were used in two pot systems (with and without plants). Carrier-free ³⁵SO₄–S was added to the soils, to provide the information on the transformations of recently added S between the different extractable S forms in soils and whether these transformations could predict plant-available S. The soils were pre-conditioned and then transferred to the glasshouse, where one set of pots were planted with perennial ryegrass (Lolium perenne L.) while the other set was left uncropped. Periodic plant harvests and soil samplings at four weekly intervals were conducted over a period of 20 weeks to determine plant S uptake and amounts of extractable soil S and ³⁵S forms using five extractants. Same extractions of soil S and ³⁵S were conducted for the initial soils. Results showed that HI-reducible and total soil S extracted by CaCl₂, KH₂PO₄ and by KCl at 40°C were utilised significantly by plants but not those extracted by NaHCO₃ and NaOH extractants. However, after the 8th week, plants continued to take up S even though levels of S extracted from the soil by CaCl₂, KH₂PO₄ and by KCl at 40°C remained low and unchanged. These results suggest that soil S taken up by plants after the 8th week period originated directly from the mineralisation of soil organic S from S pools other than those present in the extractable soil S forms. Similar results were shown by ³⁵S data, thereby confirming the complexity of determining plant S availability based on soil S extraction methods.     

Siro(haem)amide in Allochromatium vinosum and relevance of DsrL and DsrN, a homolog of cobyrinic acid a,c-diamide synthase, for sulphur oxidation

In the purple sulphur bacterium Allochromatium vinosum, the prosthetic group of dissimilatory sulphite reductase (DsrAB) was identified as siroamide, an amidated form of the classical sirohaem. The genes dsrAB are the first two of a large cluster of genes necessary for the oxidation of sulphur globules stored intracellularly during growth on sulphide and thiosulphate. DsrN is homologous to cobyrinic acid a,c diamide synthase and may therefore catalyze glutamine-dependent amidation of sirohaem. Indeed, an A. vinosumDeltadsrN in frame deletion mutant showed a significantly reduced sulphur oxidation rate that was fully restored upon complementation with dsrN in trans. Sulphite reductase was still present in the DeltadsrN mutant. DsrL is a homolog of the small subunits of bacterial glutamate synthases and was proposed to deliver glutamine for sirohaem amidation. However, recombinant DsrL does not exhibit glutamate synthase activity nor does the gene complement a glutamate synthase-deficient Escherichia coli strain. Deletion of dsrL showed that the encoded protein is absolutely essential for sulphur oxidation in A. vinosum.     

水稻土中CH4氧化的研究

在实验室条件下研究了水稻土中CH4氧化的特性 .结果表明 ,在早稻种植前采集的水稻土不能氧化大气中的CH4,但当所供给的CH4浓度 >1 0 μl·L- 1 时 ,能迅速氧化CH4,所供给的CH4浓度越高 ,氧化CH4的速度越大 .经高浓度 ( >1 0 0 0 μl·L- 1 )的CH4预培养 1 0d ,可使本来不具有氧化大气CH4能力的土壤氧化大气CH4.大田CH4排放通量高的水稻土 ,氧化CH4的能力较大 .