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.     

Sulphur oxidation in tidal mangrove soils of Sierra Leone

Summary Tidal mangrove soil contained about 17-mg/g (oven-dry soil) of oxidisable sulphur, of which about 9 mg was insoluble in acetone. Samples showed considerable variability and this was shown to be due to the fact that decayed wood in the soil was heavily impregnated with oxidisable sulphur, a high proportion of which was insoluble in acetone. It is suggested that this proportion was the polysulphide fraction.When the soil was dried, its pH value fell to 3.0 to 2.4 due to the activity of sulphur-oxidising bacteria. When the pH value of the soil fell below 3 a rapid decline in the number of the organisms present occurred, and it is suggested that this was due to the increase in the availability of ferric iron which also occurred below this pH value.CaCO₃ had two main effects on sulphur oxidation; one on the sulphur-oxidising bacteria, increasing or decreasing sulphur oxidation according to whether the pH value was moved into or out of their range of activity, and an inhibitory effect on pyrites oxidation. The results indicate that the pyrites fraction was not oxidised above pH 3 and that it was not involved in acid-formation. It is suggested that pyrites oxidation under the experimental conditions was a chemical reaction possibly involving ferric ions.The possible application of the results to the reclamation of saline mangrove swamps is discussed.     

Isolation and characterization of alkaliphilic, chemolithoautotrophic, sulphur-oxidizing bacteria

Alkaliphilic sulphur-oxidizing bacteria were isolated from samples from alkaline environments including soda soil and soda lakes. Two isolates, currently known as strains AL 2 and AL 3, were characterized. They grew over a pH range 8.0–10.4 with an optimum at 9.5–9.8. Both strains could oxidize thiosulphate, sulphide, polysulphide, elemental sulphur and tetrathionate. Strain AL 3 more actively oxidized thiosulphate and sulphide, while isolate AL 2 had higher activity with elemental sulphur and tetrathionate. Isolate AL 2 was also able to oxidize trithionate. The pH optimum for thiosulphate and sulphide oxidation was between 9–10. Some activity remained at pH 11, but was negligible at pH 7. Metabolism of tetrathionate by isolate AL 2 involved initial anaerobic hydrolysis to form sulphur, thiosulphate and sulphate in a sequence similar to that in other colourless sulphur-oxidizing bacteria. Sulphate was produced by both strains. During batch growth on thiosulphate, elemental sulphur and sulphite transiently accumulated in cultures of isolates AL 2 and AL 3, respectively. At lower pH values, both strains accumulated sulphur during sulphide and thiosulphate oxidation. Both strains contained ribulose bisphosphate carboxylase. Thiosulphate oxidation in isolate AL 3 appeared to be sodium ion-dependent. Isolate AL 2 differed from AL 3 by its high GC mol % value (65.5 and 49.5, respectively), sulphur deposition in its periplasm, the absence of carboxysomes, lower sulphur-oxidizing capacity, growth kinetics (lower growth rate and higher growth yield) and cytochrome composition.     

Dynamics of oxidation of inorganic sulphur compounds in upper soil horizons of spruce forests

Dynamics of oxidation of inorganic sulphur compounds to sulphate by the soil of spruce forests was investigated. Sulphide, sulphite and thiosulphate are oxidized to sulphate at a maximal rate at the beginning of the reaction, oxidation of elemental sulphur exhibits a lag phase. Linear relationships between the amounts of the produced sulphate and concentrations of substrates in the soil could be detected. On the basis of this finding a method for comparison of the oxidative activity of various soils was proposed.     

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.     

Effect of industrial immissions with high sulphur dioxide content on thiobacilli and oxidative activity of spruce forest soils towards inorganic sulphur compounds

Effect of industrial immissions with high sulphur dioxide content on the upper horizons of spruce forest soils in NW Bohemia was investigated. The content of sulphates, oxidative activity towards sulphide, elemental sulphur, thiosulphate and sulphite, concentration and species representation of thiobacilli in horizons F, H and A in regions highly affected by immissions (two localities) and in regions relatively less influenced (three localities) were followed. In the affected areas the sulphur content in the soil was higher, the species representation of thiobacilli was similar and their concentration was higher, the ability of the soil to oxidize thiosulphate was inhibited and oxidation of elemental sulphur was stimulated. The oxidation of sulphide and sulphite was not significantly affected by the immissions. Changes caused by immissions could be observed only in horizons F and H and did not involve horizons A.     

Biotechnological process for sulphide removal with sulphur reclamation

A new biotechnological process for sulphide removal is proposed. The process is based on the oxidation of sulphide into elemental sulphur, which can be removed by sedimentation. In this study it was found that elemental sulphur and sulphate are the main oxidation products of the biological sulphide oxidation. The settling characteristics become worse as the sulphide concentration increases, due to polysulphide formation. The start-up phase of this biological system is very short; Only four days are needed to reduce the sulphide concentration of 100 to 2 mg/l at a HRT (Residence time) of 22 minutes. Also some environmental factors were evaluated. The optimal pH is situated in the pH-range 8.0–8.5. Significantly lower conversion rates are found at pH = 6.5 to 7.5 and pH = 9.0, while at pH = 9.5 the sulphide oxidation capacity of the system detoriates. The process temperature was 20°C, although the optimal temperature is situated in the range 25–35°C. No substrate inhibition of sulphide was found at sulphide concentrations up to 100 mg/l.     

Multivariate factor analysis of sulfur oxidation and rhodanese activity in soils

The role of rhodanese as an intermediate catalyst in the oxidation of elemental S (S°) is not well understood. This study investigated the effect of 26 soil properties and steam sterilization in relation to S° oxidation and rhodanese activity in 33 soils (27 Oregon soils and six Chinese soils). S° oxidation potential was determined by incubating (7 d at 23 °C) soil amended with 500 mg S° kg^-1 soil and measuring the SO₄ released. Both total S° oxidation (TSO) and rhodanese activity varied widely among the 33 soils, ranging from 0 to 143 mg SO₄-S kg^-1 soil 7 d^-1 and 22 to 2109 nmoles SCN^- g^-1 soil h^-1 respectively. S° oxidation but not rhodanese activity had a significant positive correlation with soil pH. In sterile soils, chemical S° oxidation (CSO) averaged 3% of the total S° oxidation and apparent rhodanese activity averaged 11% of the total rhodanese activity. S° oxidation was not significantly correlated with rhodanese activity. However, development of stepwise regression models predicting S° oxidation revealed that rhodanese activity was an important explanatory variable in predicting biological S° oxidation (TSO minus CSO). Also, microbial biomass C was found to be an important parameter in models for both S° oxidation and rhodanese activity. Investigations of the effect of acidification during S° oxidation showed that biological S° oxidation was negatively correlated with S° oxidation-induced-pH-change for soils with pH > 6 but no such significant relationship was found on soils with pH> 6. This suggested that extreme acidity may inhibit S° oxidation but not rhodanese activity.     

Sulphur oxidation by soil fungi including some species of mycorrhizae and wood-rotting basidiomycetes

Abstract The mycorrhizal fungi Amanita muscaria, Paxillus involutus, Hymenoscyphus ericae, Pisolithus tinctorius, Rhizopogon roseolus , and Suillus bovinus oxidized elemental sulphur to thiosulphate and sulphate in vitro. In some, but not all cases, tetrathionate was also formed. Limited oxidation of elemental sulphur by R. roseolus also occurred when growing in association with Pinus contorta in unsterilized peat. Although yeasts capable of oxidizing sulphur could not be isolated from a wide range of soils, a yeast-like fungus ( Monilia sp.) isolated from deciduous woodland soil oxidized elemental sulphur to sulphate, forming thiosulphate, but not tetrathionate. This fungus also oxidized tetrathionate to sulphate but showed only limited ability to oxidize thiosulphate to tetrathionate. Both Aspergillus niger and Trichoderma harzianum oxidized elemental sulphur in mixed culture with Mucor flavus . Larger amounts of sulphate were initially formed in mixed, compared to single culture; but by week 5 of the incubation period sulphate formation was greatest in single culture. The wood-rotting fungi, Hypholoma fasciculare and Phanerochaete velutina showed a limited ability to oxidize elemental sulphur in vitro but were incapable of oxidizing the element when growing as mycelial cords in non-sterilized soils. The relevance of these results to the possibility that fungi play a role in sulphur oxidation in soils is commented upon.     

The evaluation of plant-available sulphur in soils. II

Summary The availability to oats of adsorbed sulphate in soils and of sulphate impurity in calcium carbonate was studied in pot-culture experiments.When calcium carbonate was added to soils with pH values ranging from 5.7 to 7.4 the uptake of sulphur by oats was increased, due probably to enhanced mineralization of soil organic sulphur. When the calcium carbonate contained sulphate impurity the uptake of sulphur was further increased by an amount comparable with the release of sulphate which could be expected from a reaction of the calcium carbonate with the exchangeable hydrogen of the soil. Sulphate in excess of this amount appeared to be largely unavailable. Uptake of sulphur by oats from calcareous sands containing large amounts of insoluble sulphate associated with calcium carbonate also suggested that soil sulphur in this form had very low availability to plants.Substantial increases in the amounts of sulphur extracted by reagents commonly used for the determination of adsorbed sulphate in soils occurred when soils were airdried at about 20°C. Decreases in adsorbed sulphate in soils following the growth of oats in pot culture confirmed that adsorbed sulphate is readily available to plants.     

Some factors influencing production of sulphate by oxidation of elemental sulphur and thiosulphate in upper horizons of spruce forest soils

Some factors influencing the oxidative activity of upper horizons of spruce forest soils (a mixture of fermentative and humus layers) toward intermediates of the oxidative part of the sulphur cycle were investigated. Preincubation of the soil with added cysteine, sulphide, elemental sulphur or thiosulphate was found to stimulate enzyme systems oxidating any of these compounds. Sulphite and sulphate were ineffective in this respect. The oxidation of elemental sulphur was stimulated by CaCO3, technical urea and high doses of superphosphate and potassium sulphate. It was inhibited by KH2PO4, pure urea, 40 % potassium salt, ammonium nitrate with calcium carbonate and the fertilizer NPK I. It proceeded at the highest rate at approximately 60 % capillary capacity (61 % of mass water content). Oxidation of thiosulphate was stimulated by KH2PO4, pure urea, superphosphate, potassium sulphate and only slightly by the fertilizer NPK I. It was inhibited by CaCO3, 40 % potassium salt and only slightly by ammonium nitrate with calcium carbonate. Potassium chloride, glucose and technical urea were without effect. The oxidation proceeded at the highest rate at 35 % maximal capillary capacity (48 % mass water content).     

The removal of pyritic sulphur from coal by Leptospirillum-like bacteria

Summary The microbial oxidation of pyritic sulphur was studied in a 4.5-l airlift fermentor at pH 1.5 and 100 g/l pulp density. By microbial leaching with Leptospirillum-like bacteria 85% of the pyritic sulphur was removed within 40 days; 30% of the removed pyrite was oxidized to elemental sulphur, the rest being transformed to soluble sulphate. Accumulation of elemental sulphur could be avoided by using a mixed culture of Leptospirillum-like bacteria and Thiobacillus ferrooxidans. Apart from oxidation of elemental sulphur neither the pure nor the mixed culture showed a significant difference as to removal of pyrite.     

Growth of Wolinella succinogenes with polysulphide as terminal acceptor of phosphorylative electron transport

Polysulphide was formed according to reaction (1), when tetrathionate was (1) $${\text{S}}_4 {\text{O}}_6^{2 - } + {\text{HS}}^ - \to 2{\text{S}}_2 {\text{O}}_3^{2 - } + {\text{S(O)}} + {\text{H}}^ + $$ added to an anaerobic buffer (pH 8.5) containing excess sulphide. S(O) denotes the zero oxidation state sulphur in the polysulphide mixture S _infn ^sup2- . The addition of formate to the polysulphide solution in the presence of Wolinella succinogenes caused the reduction of polysulphide according to reaction (2). The bacteria grew in a medium containing formate and sulphide, (2) $${\text{HCO}}_2^ - + {\text{S(O)}} + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + {\text{HS}}^ - + {\text{H}}^ + $$ when tetrathionate was continuously added. The cell density increased proportional to reaction (3) which represents the sum of reactions (1) and (3) $${\text{HCO}}_2^ - + {\text{S}}_{\text{4}} {\text{O}}_6^{2 - } + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + 2{\text{S}}_{\text{2}} {\text{O}}_3^{2 - } + 2{\text{H}}^ + $$ (2). The cell yield per mol formate was nearly the same as during growth on formate and elemental sulphur, while the velocity of growth was greater. The specific activities of polysulphide reduction by formate measured with bacteria grown with tetrathionate or with elemental sulphur were consistent with the growth parameters. The results suggest that W. succinogenes grow at the expense of formate oxidation by polysulphide and that polysulphide is an intermediate during growth on formate and elemental sulphur.     

Contribution to the chemical and bacteriological oxidation of pyrite in soil

Summary 1. The rate of pyrite oxidation and the influence of microbes on this process were studied, since this oxidation proved to be one of the most important phenomena in the process of weathering and aging of newly reclaimed marine soils.2. Pyrite oxidation does not depend on the activity of microbes, but is significantly stimulated by the metabolism of the specific sulphur-oxidising bacteria. The most important species proved to beThiobacillus thiooxidans, the same organism that takes part in the oxidation of monosulphides, thiosulphates, etc.3. Factors depressing the solubility of iron (high pH level or high concentration of phosphate ions) retard the oxidation of pyrite.4. It is probable that the oxidative disintegration of pyrite starts with the oxidation of the ferrous ions on the surface of the crystals, releasing the sulphur. The latter is then oxidised primarily by the specific sulphur-oxidising microbes and transformed to sulphates.     

Iron oxidation stimulates organic matter decomposition in humid tropical forest soils

Humid tropical forests have the fastest rates of organic matter decomposition globally, which often coincide with fluctuating oxygen (O₂) availability in surface soils. Microbial iron (Fe) reduction generates reduced iron [Fe(II)] under anaerobic conditions, which oxidizes to Fe(III) under subsequent aerobic conditions. We demonstrate that Fe (II) oxidation stimulates organic matter decomposition via two mechanisms: (i) organic matter oxidation, likely driven by reactive oxygen species; and (ii) increased dissolved organic carbon (DOC) availability, likely driven by acidification. Phenol oxidative activity increased linearly with Fe(II) concentrations (P < 0.0001, pseudo R² = 0.79) in soils sampled within and among five tropical forest sites. A similar pattern occurred in the absence of soil, suggesting an abiotic driver of this reaction. No phenol oxidative activity occurred in soils under anaerobic conditions, implying the importance of oxidants such as O₂ or hydrogen peroxide (H₂O₂) in addition to Fe(II). Reactions between Fe(II) and H₂O₂ generate hydroxyl radical, a strong nonselective oxidant of organic compounds. We found increasing consumption of H₂O₂ as soil Fe(II) concentrations increased, suggesting that reactive oxygen species produced by Fe(II) oxidation explained variation in phenol oxidative activity among samples. Amending soils with Fe(II) at field concentrations stimulated short‐term C mineralization by up to 270%, likely via a second mechanism. Oxidation of Fe(II) drove a decrease in pH and a monotonic increase in DOC; a decline of two pH units doubled DOC, likely stimulating microbial respiration. We obtained similar results by manipulating soil acidity independently of Fe(II), implying that Fe(II) oxidation affected C substrate availability via pH fluctuations, in addition to producing reactive oxygen species. Iron oxidation coupled to organic matter decomposition contributes to rapid rates of C cycling across humid tropical forests in spite of periodic O₂ limitation, and may help explain the rapid turnover of complex C molecules in these soils.     

The effect of sodium chloride and sulphate on sulphur oxidation in soil

Summary The effect of sodium chloride on sulphur oxidation in Terra Rossa and Rendzina soils was studied by incubation and perfusion techniques. Sulphur oxidation was observed at concentrations up to 8 per cent NaCl, but was completely arrested at 10 per cent sodium chloride. Sodium chloride caused a delay in the onset of sulphur oxidation, its rate being only slightly affected. A relationship between sulphate appearance and decrease in pH was observed only in sulphur-amended Terra Rossa soil. Under optimal conditions, 53 and 54 per cent of added sulphur (5000 ppm) was recovered as SO₄-S from the Terra Rossa and Rendzina soils, respectively. This maximal level of sulphate production was only slightly affected by the addition of sulphate up to 3000 ppm S.It was concluded that inhibition in further sulphur oxidation was not caused by sulphate accumulation.     

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.     

Methane consumption by montane soils: implications for positive and negative feedback with climatic change

We report here three years of field observations of methane uptake, averaging 1.2 mg CH₄ m^–2 d^–1 in montane meadow soils. Surface soil moisture influenced diffusion of substrate while in deeper soil, where methane oxidation was maximum, moisture influenced both diffusion and microbial activity. Microbial oxidation of methane was maximum at an intermediate level of soil moisture, at this site at about 25% moisture by weight (50% water holding capacity). Laboratory incubations also showed inhibition below 20% moisture. These results provide in situ characterization of moisture limitation of methanotroph activity and evidence that soil drying may diminish the methane sink strength. The microbial limitation to methane consumption at low soil moisture provides a mechanism for positive feedback between methane flux and climate warming, as suggested by ice core data (Blunier et al. 1993; Chappellaz et al. 1990; Stauffer et al. 1985).     

Some factors affecting the mineralization of organic sulphur in soils

Summary Factors affecting the release of sulphate from a number of eastern Australian soils were studied.All of the soils released sulphate when dried. The amounts released were influenced by the manner in which the soil was dried. Air-drying in the laboratory at 20°C released least sulphate.Sulphate was mineralized in all soils by incubation at 30°C but the amounts mineralized could not be related to soil type or any single soil property. The ratio of nitrogen mineralized: sulphur mineralized varied widely between soils and was generally appreciably greater than the ratio of total nitrogen: organic sulphur in the soils.A rapid flush of mineralization of both sulphur and nitrogen took place when some of the soils were rewetted and incubated after they had been dried in the laboratory and stored for 4 to 5 months. Following this, the rate of mineralization was similar to that in the original undried soil. During this flush, the enhancement of sulphur mineralization was relatively greater than that of nitrogen so that the ratio of nitrogen mineralized: sulphur mineralized was considerably smaller than that during later phases of the incubation or that of the original moist soil. Soils collected after they had remained dry in the field for a similar period of time did not show this type of mineralization although they had initially done so when collected moist and air-dried in the laboratory.The effects of temperature, soil moisture, toluene and formaldehyde, and the addition of calcium carbonate to soils on the mineralization of sulphur were similar to their effects on the mineralization of nitrogen.     

The evaluation of plant-available sulphur in soils

Summary Examination of a range of naturally occurring calcium carbonates and calcareous soils has shown that insoluble sulphate associated with calcium carbonate may comprise an important fraction of soil sulphur. One soil contained as much as 93 per cent of its sulphur in this form. It seems likely that this sulphate occurs as a co-precipitated or co-crystallized impurity in the calcium carbonate.Most surface soils had only low capacity to adsorb sulphate and contained only small amounts of sulphur in this form. Two acid surface soils and many acid subsoils, however, adsorbed sulphate quite strongly and in some acid subsoil clays adsorbed sulphate made up an important fractions of the total sulphur.Sulphate adsorption was found to be negligible above pH 6.5 and adsorbed sulphate may be determined by aqueous extraction after increasing the pH above this value by addition of solid calcium carbonate. Adsorption of sulphate during acid extraction of soils can lead to low values in the determination of acid-soluble sulphates. Sulphate so adsorbed can be determined by a second extraction with water after the addition of solid calcium carbonate to increase the pH to a value greater than 6.5.