Sulphur Oxidation In Soils Research Articles

Effects of pH and ionic strength on elemental sulphur oxidation in soil

Elemental S oxidation in soil is a microbially mediated process and is hypothesised to be influenced by changes to soil chemical properties such as acidity and ionic strength, which may arise from co-granulation with macronutrients or elemental S oxidation itself. Soil incubation was conducted with a sandy soil from South Australia to assess the effect of acidification and increased ionic strength on bacterial abundance and community composition and on elemental S oxidation during a 14-week incubation at 25 °C and 70% field capacity. Prior to incubation, the soil was treated with HNO3 to bring the pH to 6.7–4.4 or with KH2PO4 to increase the ionic strength by 0–0.7 M. Elemental S was applied at 200 mg kg−1 air-dried soil. Acidification or increased ionic strength had no or little effect on elemental S oxidation but decreased the abundances of 16S ribosomal deoxyribonucleic acid (rRNA) and soxB genes and changed the bacterial community composition. A second experiment with two other soils also showed that acidification did not, or only slightly, decreased elemental S oxidation, even though acidification strongly reduced 16S rRNA and soxB gene abundances in one of the soils. This study suggests that shifts in bacterial population brought about by temporary changes in pH and ionic strength, as may occur around fertiliser granules, have no or little effect on elemental S oxidation, indicating that the S-oxidising bacterial community in these agricultural soils contains functionally redundant taxa, which responded to changing conditions.

DISTRIBUTION OF HAEMOLYTIC THIOBACILLI IN SEWAGE SAMPLES

Sulphur is one of the essential plant nutrients and it contributes to yield and quality of crops. Thiobacillus play an important role in sulphur oxidation in soil and domestic wastewater.The present study is sought to understand the frequency of Thiobacillus in sewage water samples collected from hospital and domestic area.Distribution of sulphur oxidizing bacteria were analysed by using modified Thiobacilli agar. Five isolates were selected and analysed their selected putative virulence properties phenotypically.Also they were showed biocompatible within the group of the Thiobacilli.The extracellular products (culture supernatant) of Thiobacilli showed a substantial level of haemolytic activity and antagonistic activity. Among the isolates from sewage sources, TB-D1 and TB-D2 produced higher level of bacteriocin against pathogenic bacteria due to the formation of maximum inhibition zone. It reveals that the bacteriocin from Thiobacillus showed the elevated antagonistic activity against most of the pathogenic bacteria, as we tested.The strains TB-D4 and TB-D5 showed beta and alpha haemolysis, it might have virulent properties and cause infection in human and animals.The strain TB-D5 showed the maximum inhibitions while compared with others. It is visibly showing presence of virulence factors in the extracellular metabolites of Thiobacilli.

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

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.

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

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.

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

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.

Sulphur oxidation by fungi

Aspergillus niger oxidized elemental sulphur in vitro to form relatively large amounts of sulphate, initially producing thiosulphate, but not tetrathionate. Growth was inhibited by thiosulphate, but not by elemental sulphur, although both were oxidized to sulphate. Mucor flavus also oxidized elemental sulphur, but while it produced less sulphate than A. niger , it consistently formed both thiosulphate and tetrathionate. Substantial sulphur oxidation by Trichoderma harzianum occurred only when large amounts of sucrose were provided, but it was able to oxidize elemental sulphur in autoclaved soil and to use straw to support sulphur oxidation in vitro. The relevance of these findings to the oxidation of sulphur in soils by fungi is discussed.

Effects of lindane, captan and malathion on nitrification, sulphur oxidation, phosphate solubilisation and respiration in a tropical soil

Additions of lindane (100 mg kg −1), captan (100 mg kg −1) or malathion (50 mg kg −1) to an agricultural soil in the laboratory did not affect the soil microflora much but some of their activities were affected by the xenobiotics. Captan increased the rate of soil respiration by 7% while lindane and malathion slowed this process by 11 and 6%, respectively. The rate of phosphate solubilisation was decreased by 50% by captan in 15 days. In lindane- and malathion-treated soils, the rates were decreased to 34 and 3%, respectively, of the normal rate. None of these effects lasted longer than 30 days. Malathion increased the rate of sulphur oxidation in soil by 8% and lindane and captan affected this reaction adversely by 10 and 3%, respectively. Nitrification was repressed by all three pesticides for at least 30 days in the soil. Results suggest that only malathion produced breakdown products inhibitory to the nitrification process.

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.

Use of respirometry to evaluate sulphur oxidation in soils

Conventional Warburg respirometric techniques were used to evaluate sulphur-oxidizing activity in soils derived from sediments deposited in brackish environments. Experiments were carried at 30° C on fresh samples dried under vacuum or a warm draught, and enriched either with thiosulphate or with elemental S. By difference from the respiration of the non-enriched sample, a rate of S oxidation was calculated. This rate was higher when the soil was moistened by a 1% solution (v/v) of Tween 80 than when water alone was used. Sublimed elemental S was a better substrate than thiosulphate for the measurement of S oxidizing activity. In all samples, the rate of S oxidation was correlated with counts of autotrophic S oxidizing microorganisms. ( Thiobacillus sp) on selective agar.

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

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.

Oxidation of sulphur in soils

This paper reviews briefly the forms of sulphur in soils and discusses the factors affecting the oxidation of this sulphur to other oxidation states. This oxidation is believed to be carried out mainly be micro-organisms but in many cases strictly chemical reactions are involved. Invironmental factors such as temperature, moisture, and pH, as well as microbial population and particle size influence the rate of sulphur oxidation in soil. Plants normally absorb sulphur in the form of sulphate, and thus the oxidation of sulphide, elemental sulphur and organic sulphur is of prime importance in plant nutrition.