Observations on the source of acid in empoldered mangrove soils

Summary Formation of elemental sulphur as an intermediate in polysulphide oxidation in mangrove soils has been demonstrated both in laboratory experiments and in the field. The oxidation of soil polysulphides occurred in the absence of more reactive sulphur compounds and it is suggested that these are not essential for the initiation of sulphur oxidation in high sulphur soils. Field experiments contained some evidence of instability of soil polysulphides at pH values near neutrality, but laboratory experiments suggested that early decomposition of polysulphides may be accelerated by non-biological oxidations which lower the soil pH value.Maximum population ofThiobacillus thio-oxidans was reached much earlier than maximum oxidative activity, although an early peak in oxidative activity could be obtained by adding elemental sulphur to soil. It is suggested that while conditions in the early stages of the oxidation may be suitable for multiplication of the organisms, maximum oxidative activity is limited by the rate of release of sulphur from the decomposing polysulphide.     

Some differences between the soils ofRhizophora andAvicennia mangrove swamps in sierra leone

Summary The differences existing between a fibrous mud from aRhizophora mangrove swamp and a non-fibrous mud from a nearbyAvicennia swamp have been examined.The differences found between the muds are due largely to the kind of mangrove they support.Compared to the Avicennia swamp mud, that from the Rhizophora swamp had a higher pH value and a higher content of oxidisable sulphur, nitrogen, phosphorus, and carbon. The behaviour of the muds on incubation has helped to explain why the mud under Rhizophora is considered as being more fertile than mud under Avicennia. An apparent high rate of decomposition of the Rhizophora swamp mud as compared to that of mud under Avicennia was due to high oxygen uptake during sulphur oxidation. Rhizophora-bearing mud had a very high C/N ratio and inorganic nitrogen added to it was immobilised. It is suggested that land reclaimed from Rhizophora would respond to nitrogen fertilization. The most important difference between the muds was in their behaviour on drying. The intense acidity produced by sulphur oxidation in the fibrous mud affected all other changes, chemical and microbiological. It was found that if the moisture content of the fibrous mud remained at any point between 40 and 10 per cent for any length of time, then the mud became more acid than if continuously dried.     

Biogeochemical cycling of iron and sulphur in leaching environments

Abstract: Bacterial dissimilatory reduction of iron and sulphur in extremely acidic environments is described. Evidence for reduction at two disused mine sites is presented, within stratified 'acid streamers' growths and in sediments from an acid mine drainage stream. A high proportion (approx. 40%) of mesophilic heterotrophic acidophiles were found to be capable of reducing ferric iron (soluble and insoluble forms) under microaerophilic and anoxic conditions. Mixed cultures of Thiobacillus ferrooxidans and Acidiphilium -like isolate SJH displayed cycling of iron in shake flask and fermenter cultures. Oxido-reduction of iron in mixed cultures was determined by oxygen concentration and availability of organic substrates. Some moderately thermophilic iron-oxidis- ing bacteria were also shown to be capable of reducing ferric iron under conditions of limiting oxygen when grown in glycerol/yeast extract or elemental sulphur media. Cycling of iron was observed in pure cultures of these acidophiles. Sulphate-reducing bacteria isolated from acid streamers could be grown in acidified glycerol/yeast extract media (as low as pH 2.9), but not in media used conventionally for their laboratory culture. An endospore-forming, non-motile rod resembling Desulfotomaculum has been isolated. This bacterium has a wide pH spectrum, and appears to be acid-tolerant rather than acidophilic.     

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.     

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.     

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.     

Microbiological Leaching of Metallic Sulfides

The percentage of chalcopyrite leached in percolators by Thiobacillus ferrooxidans was dependent on the surface area of the ore but not on the amount. Typical examples of ore leaching, which demonstrate the role of the bacteria, are presented. In stationary fermentations, changes in KH(2)PO(4) concentration above or below 0.1% decreased copper leaching as did reduction in the MgSO(4).7H(2)O and increase in the (NH(4))(2)SO(4) concentration. Bacterial leaching of chalcopyrite was more effective than nonbiological leaching with ferric sulfate; ferric sulfate appeared to retard biological leaching, but this effect was likely caused by formation of an insoluble copper-iron complex. Ferrous sulfate and sodium chloride singly accentuated both bacterial and nonbiological leaching of chalcocite but jointly depressed bacterial action. Sodium chloride appeared to block bacterial iron oxidation without interfering with sulfide oxidation. Bacterial leaching of millerite, bornite, and chalcocite was greatest at pH 2.5. The economics of leaching a number of British Columbia ore bodies was discussed.     

Optimal conditions for bio-oxidation of ferrous ions to ferric ions using Thiobacillus ferrooxidans

A chemo-biochemical process using Thiobacillus ferrooxidans for desulphurization of gaseous fuels and emissions containing hydrogen sulphide (H2S) has been developed. In the first stage, H2S present in fuel gas and emissions is selectively oxidized to elemental sulphur using ferric sulphate. The ferrous sulphate produced in the first stage of the process is oxidized to ferric sulphate using Thiobacillus ferrooxidans for recycle and reuse in the process. The effects of process variables, temperature, pH, total dissolved solids (TDS), elemental sulphur, ferric and magnesium ions on bio-oxidation of ferrous ions to ferric ions were investigated using flask culture experiments. The bio-oxidation of ferrous ions to ferric ions could be achieved efficiently in the temperature range of 20(+/-1)-44(+/-1) degrees C. A pH range of 1.8(+/-0.02)-2.2(+/-0.02) was optimum for the growth of culture and effective bio-oxidation of ferrous ions to ferric ions. The effect of TDS on bio-oxidation of ferrous ions indicated that a preacclimatized culture in a growth medium containing high dissolved solid was required to achieve effective bio-oxidation of ferrous ions. Elemental sulphur ranging from 1000 to 100,000 mg/l did not have any effect on efficiency of ferrous ion oxidation. The efficiency of bio-oxidation of ferrous ions to ferric ions was not affected in the presence of ferric ions up to a concentration of 500 mg/l while 3 mg/l of magnesium ion was optimal for achieving effective bio-oxidation.     

Natural occurrence of microbial sulphur oxidation by long-range electron transport in the seafloor

Recently, a novel mode of sulphur oxidation was described in marine sediments, in which sulphide oxidation in deeper anoxic layers was electrically coupled to oxygen reduction at the sediment surface. Subsequent experimental evidence identified that long filamentous bacteria belonging to the family Desulfobulbaceae likely mediated the electron transport across the centimetre-scale distances. Such long-range electron transfer challenges some long-held views in microbial ecology and could have profound implications for sulphur cycling in marine sediments. But, so far, this process of electrogenic sulphur oxidation has been documented only in laboratory experiments and so its imprint on the seafloor remains unknown. Here we show that the geochemical signature of electrogenic sulphur oxidation occurs in a variety of coastal sediment environments, including a salt marsh, a seasonally hypoxic basin, and a subtidal coastal mud plain. In all cases, electrogenic sulphur oxidation was detected together with an abundance of Desulfobulbaceae filaments. Complementary laboratory experiments in intertidal sands demonstrated that mechanical disturbance by bioturbating fauna destroys the electrogenic sulphur oxidation signal. A survey of published geochemical data and 16S rRNA gene sequences identified that electrogenic sulphide oxidation is likely present in a variety of marine sediments with high sulphide generation and restricted bioturbation, such as mangrove swamps, aquaculture areas, seasonally hypoxic basins, cold sulphide seeps and possibly hydrothermal vent environments. This study shows for the first time that electrogenic sulphur oxidation occurs in a wide range of marine sediments and that bioturbation may exert a dominant control on its natural distribution.     

Soil Respiration and Belowground Carbon Allocation in Mangrove Forests

Mangrove forests cover large areas of tropical and subtropical coastlines. They provide a wide range of ecosystem services that includes carbon storage in above- and below ground biomass and in soils. Carbon dioxide (CO₂) emissions from soil, or soil respiration is important in the global carbon budget and is sensitive to increasing global temperature. To understand the magnitude of mangrove soil respiration and the influence of forest structure and temperature on the variation in mangrove soil respiration I assessed soil respiration at eleven mangrove sites, ranging from latitude 27°N to 37°S. Mangrove soil respiration was similar to those observed for terrestrial forest soils. Soil respiration was correlated with leaf area index (LAI) and aboveground net primary production (litterfall), which should aid scaling up to regional and global estimates of soil respiration. Using a carbon balance model, total belowground carbon allocation (TBCA) per unit litterfall was similar in tall mangrove forests as observed in terrestrial forests, but in scrub mangrove forests TBCA per unit litter fall was greater than in terrestrial forests, suggesting mangroves allocate a large proportion of their fixed carbon below ground under unfavorable environmental conditions. The response of soil respiration to soil temperature was not a linear function of temperature. At temperatures below 26°C Q10 of mangrove soil respiration was 2.6, similar to that reported for terrestrial forest soils. However in scrub forests soil respiration declined with increasing soil temperature, largely because of reduced canopy cover and enhanced activity of photosynthetic benthic microbial communities.     

Methods for the isolation and purification of ethanol-insoluble,phenolic esters in Mentha arvensis

Previous kinetic, isotopic studies have suggested that ‘insoluble’ phenolic esters may be precursors of lignin. Heretofore, the ‘insoluble’ esters have been detected by the chromatographic examinations of gross hydrolysis products of ethanol-insoluble resides and/or acetone powders. We have developed new methods for the isolation and purification of certain of the ethanol-insoluble, phenolic esters of Mentha arvensis. ‘Insoluble’ conjugates of caffeic, ferulic and p-coumaric acids were purified and were shown to be electro-phoretically and chromatographically homogeneous. These compounds were distinguished on the basis of their anionic mobility at pH 1·9. A second pool of caffeic acid was associated with a high MW fraction. Two acylated anthocyanins containing p-coumaric acid and caffeic acid were also obtained from acetone powders.     

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.     

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.     

Microbial carbon metabolism associated with electrogenic sulphur oxidation in coastal sediments

Recently, a novel electrogenic type of sulphur oxidation was documented in marine sediments, whereby filamentous cable bacteria (Desulfobulbaceae) are mediating electron transport over cm-scale distances. These cable bacteria are capable of developing an extensive network within days, implying a highly efficient carbon acquisition strategy. Presently, the carbon metabolism of cable bacteria is unknown, and hence we adopted a multidisciplinary approach to study the carbon substrate utilization of both cable bacteria and associated microbial community in sediment incubations. Fluorescence in situ hybridization showed rapid downward growth of cable bacteria, concomitant with high rates of electrogenic sulphur oxidation, as quantified by microelectrode profiling. We studied heterotrophy and autotrophy by following ¹³C-propionate and -bicarbonate incorporation into bacterial fatty acids. This biomarker analysis showed that propionate uptake was limited to fatty acid signatures typical for the genus Desulfobulbus. The nanoscale secondary ion mass spectrometry analysis confirmed heterotrophic rather than autotrophic growth of cable bacteria. Still, high bicarbonate uptake was observed in concert with the development of cable bacteria. Clone libraries of 16S complementary DNA showed numerous sequences associated to chemoautotrophic sulphur-oxidizing Epsilon- and Gammaproteobacteria, whereas ¹³C-bicarbonate biomarker labelling suggested that these sulphur-oxidizing bacteria were active far below the oxygen penetration. A targeted manipulation experiment demonstrated that chemoautotrophic carbon fixation was tightly linked to the heterotrophic activity of the cable bacteria down to cm depth. Overall, the results suggest that electrogenic sulphur oxidation is performed by a microbial consortium, consisting of chemoorganotrophic cable bacteria and chemolithoautotrophic Epsilon- and Gammaproteobacteria. The metabolic linkage between these two groups is presently unknown and needs further study.     

Violet-Pigmented Pseudomonads With Antifungal Activity From the Rhizosphere of Beans

Bean rhizosphere bacteria antagonistic to four root-infecting fungi and an antibiotic produced by these bacteria were studied. The bacteria were violet-pigmented gram-negative rods, probably belonging to the genus Pseudomonas. The antibiotic, which was localized largely in the bacterial cell mass, was easily extracted with acetone. It was selectively active against a wide variety of plant-pathogenic and saprophytic fungi tested in vitro but was relatively inactive against bacteria. The compound, partially purified by chromatography, was soluble in all organic solvents tried, but nearly insoluble in water. It demonstrated no characteristic ultraviolet- or visible-absorption spectrum and was chemically unidentified. The antagonistic bacteria or crude antibiotic applied to buried buckwheat segments suppressed the colonization of this substrate by Rhizoctonia spp. The data suggested that the bacteria or the antibiotic may play a role in the suppression of root-infecting fungi in soil.     

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.     

Patterns of pyrite oxidation by different microorganisms

The bacterial-chemical oxidation of natural pyrites with different physical, chemical, and electrophysical characteristics by bacteria Acidithiobacillus ferrooxidans, Sulfobacillus thermotolerans, and the archaeon Ferroplasma acidiphilum were studied. The electrophysical characteristics of three natural pyrites differed in the K _thermoEMF value (pyrites 3, 4, hole conduction (p-type conductivity); pyrite 5, mixed type conductivity (n-p)) and in the logarithm of electric resistance. Chemical oxidation of pyrites 3 and 5 resulted in no changes of K _thermoEMF. When pyrite 4 was oxidized chemically, the K _thermoEMF values remained in the same range as in the initial sample, but the ratio of grains with different K _thermoEMF values in the sample was changed: the number of grains with a higher K _thermoEMF value increased. The same changes were also observed in the course of bacterio-chemical oxidation of pyrite 4. Of the three pyrites studied, an increase in the logarithm of resistance was observed only for chemical oxidation of pyrite 4 at 28°C. At higher experimental temperatures, the logarithm of resistance increased accordingly; more active bacterial-chemical oxidation resulted in a more pronounced increase in the logarithm of resistance than chemical oxidation. On bacterial-chemical oxidation of pyrites 3 and 5 by A. ferrooxidans and S. thermotolerans strains, iron was leached more actively than sulfur. Preferred bacterial-chemical oxidation of certain fractions from the pyrite samples was shown, namely of the pyrite 3 fraction with higher K _thermoEMF values by the F. acidiphilum strain and of a fraction from the pyrite 5 sample with medium K _thermoEMF values by the A. ferrooxidans and S. thermotolerans strains. The comparative assessment of bacterial-chemical pyrite oxidation by three types of microorganisms showed the direction of changes in the K _thermoEMF values to be the same in the case of bacteria Acidithiobacillus ferrooxidans and Sulfobacillus thermotolerans and different in the case of the archaeon Ferroplasma acidiphilum.     

Wheat, canola and grain legume access to soil phosphorus fractions differs in soils with contrasting phosphorus dynamics

Despite the high phosphorus (P) mobilizing capacity of many legumes, recent studies have found that, at least in calcareous soils, wheat is also able to access insoluble P fractions through yet unknown mechanism(s). We hypothesized that insoluble P fractions may be more available to non-legume plants in alkaline soils due to increased dissolution of the dominant calcium(Ca)-P pool into depleted labile P pools, whereas non-legumes may have limited access to insoluble P fractions in iron(Fe)- and aluminium(Al)-P dominated acid soils. Four crop species (faba bean, chickpea, wheat and canola) were grown on two acid and one alkaline soil under glasshouse conditions to examine rhizosphere processes and soil P fractions accessed. While all species generally depleted the H₂O-soluble inorganic P (water Pi) pool in all soils, there was no net depletion of the labile NaHCO₃-extractable inorganic P fraction (NaHCO₃ Pi) by any species in any soil. The NaOH-extractable P fraction (NaOH Pi) in the alkaline soil was the only non-labile Pi fraction depleted by all crops (particularly canola), possibly due to increases in rhizosphere pH. Chickpea mobilized the insoluble HCl Pi and residual P fractions; however, rhizosphere pH and carboxylate exudation could not fully explain all of the observed Pi depletion in each soil. All organic P fractions appeared highly recalcitrant, with the exception of some depletion of the NaHCO₃ Po fraction by faba bean in the acid soils. Chickpea and faba bean did not show a higher capacity than wheat or canola to mobilize insoluble P pools across all soil types, and the availability of various P fractions to legume and non-legume crops differed in soils with contrasting P dynamics.     

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.     

Ratio of biological and chemical oxidation during the aerobic elimination of sulphide by colourless sulphur bacteria

Summary Culture conditions were evaluated for their relevance to chemical and biological oxidation of sulphide in aqueous solution. With a mixed culture of colourless sulphur bacteria sulphide oxidation was investigated over a concentration range of 0.005 to 3.5 mm S^2–, a pH range from 1.0 to 9.0 and temperatures from 10 to 40° C. Biological sulphide oxidation quickly decreased when fermentation conditions were suboptimal and the proportion of chemical oxidation increased with high pH values and sulphide concentration and increasing temperature. The optimal conditions for biological activity were found to be 3 mm S^2–, pH 7.0, and a mesophilic temperature (40° C).Offprint requests to: C. Plas