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.     

Macrobenthic–mud relations strengthen the foundation for benthic index development: A case study from shallow,temperate New Zealand estuaries

Globally the input of sediment to coastal systems, in particular to estuaries, is predicted to increase due to anthropogenic activities. Sediment mud content is a powerful driver of ecologically important, macrobenthic taxa in estuarine intertidal flats. Accordingly, forecasting species responses to increased sedimentation is fundamental for effective ecosystem management, particularly for productive, geologically young, and sand-dominated estuaries that characterise many countries, including New Zealand (NZ). Modelling studies have highlighted the non-linear, highly variable responses of taxa to mud concentration. However, existing taxon-specific models have not adequately accounted for the full mud gradient, the influence of potentially confounding variables (e.g. organic enrichment, heavy metal concentrations), or regional differences in species responses. Furthermore, such models are often based on qualitative expert consensus of the membership of taxa in ecological groups that characterise their sensitivity to mud content. In this study, data from 25 unmodified to highly disturbed, shallow NZ estuaries, were used to develop an ecologically relevant model to relate the responses of 39 taxa to sediment mud content for use in the intertidal flats of shallow, temperate estuaries. Preliminary analyses indicated that sediment mud content was the dominant driver of macroinvertebrate community composition among sites, total organic carbon was of secondary importance and heavy metals did not explain significant variation in composition. Regression analysis revealed a significant linear relationship between sediment mud and total organic carbon content, which permitted subsequent analyses to be based on mud content alone. Generalised additive models were used to develop taxon-specific models that, according to k-fold cross validation, accurately predicted both probability of presence (up to 79% deviance explained) and maximum density (up to 96% deviance explained) along the sediment mud gradient (0.1–92.3%). Estimates of “optimal mud range” and “distribution mud range” were quantitatively-derived for each taxon and used to categorise taxa into one of five ecological groups (identical to those used in existing biotic indices), based on their individual sensitivities to increasing mud content. By removing expert consensus from the grouping process, the classification methods established herein provide strong support for the use of quantitative indices for the assessment and management of estuarine condition in response to increasing sediment mud content. The findings indicate that NZ estuarine sediments (2–25% mud) support a more diverse and abundant macroinvertebrate assemblage and exhibit low organic enrichment (<1% total organic carbon) compared to estuaries with >25% mud content.     

Sulphur mineralization and adsorption in soils

Summary Studies were conducted to determine the comparative sulphur mineralizing capacity of selected Malaysian and Iowan soils and to determine the amounts of available and adsorbed sulphate in a number of Malaysian soils. Results of the mineralization study indicated that more sulphur mineralised from Malaysian soils although their average contents of total sulphur were lower compared to Iowan Soils. For both sets of soils, significant correlations between contents of organic carbon and total sulphur existed indicating that most of the sulphur was in organic combination. Phosphate solution consistently extracted higher quantities of sulphate in comparison to chloride solution in the Malaysian surface soils implying that a portion of the sulphate existed in adsorbed form. Adsorption of sulphate in soils was found to be dependent on concentration of sulphate added and followed the Langmuir adsorption isotherm.     

Marinobacterium sp. strain DMS-S1 uses dimethyl sulphide as a sulphur source after light-dependent transformation by excreted flavins

Marinobacterium sp. strain DMS-S1 is a unique marine bacterium that can use dimethyl sulphide (DMS) as a sulphur source only in the presence of light. High-performance liquid chromatography (HPLC) analyses of the culture supernatant revealed that excreted factors, which could transform DMS to dimethyl sulphoxide (DMSO) under light, are FAD and riboflavin. In addition, FAD appeared to catalyse the photolysis of DMS to not only DMSO but also methanesulphonate (MSA), formate, formaldehyde and sulphate. As strain DMS-S1 can use sulphate and MSA as a sole sulphur source independently of light, the excretion of flavins appeared to support the growth on DMS under light. Furthermore, three out of 12 marine bacteria from IAM culture collection were found to be able to grow on DMS with the aid of photolysis by the flavins excreted. This is the first report that bacteria can use light to assimilate oceanic organic sulphur compounds outside the cells by excreting flavins as photosensitizers.     

Sulphate reduction and sulphur cycling in lake sediments: a review

1. The concentration of sulphate is low in lakes and sulphur cycling has often been neglected in studies of organic matter diagenesis in lake sediments. The cycling of sulphur is, however, both spatially and temporally dynamic and strongly influences many biogeochemical reactions in sediments, such as the binding of phosphorus. This review examines the control of sulphate reduction and sulphur cycling in sediments of lakes with different trophic status. 2. The factors that control the rate of sulphate reduction have not been identified with certainty in the various environments because many factors are involved, e.g. oxygen and sulphate concentrations, temperature and organic matter availability. 3. Sulphate reduction is less significant under oligotrophic conditions, where mineralization is dominated by oxic decomposition. The supply of organic matter may not be sufficient to support sulphate reduction in the anoxic parts of sediments and, also, sulphate availability may control the rate as the concentration is generally low in oligotrophic lakes. 4. There is a potential for significant sulphate reduction in eutrophic lakes, as both the availability of organic matter and sulphate concentration are often higher than in oligotrophic lakes. Sulphate is rapidly depleted with sediment depth, however, and methanogenesis is generally the most important process in overall carbon mineralization. Sulphate reduction is generally low in acidic lakes because of low sulphate availability and reduced microbial activity. 5. It is still unclear which of the forms of sulphur deposits are the most important and under which conditions burial occurs. Sulphur deposition is controlled by the rate of sulphate reduction and reoxidation. Reoxidation of sulphides occurs rapidly through several pathways, both under oxic and anoxic conditions. Only a few studies have been able to examine the importance of reoxidation, but it is hypothesized that most of the reoxidation takes place under anoxic conditions and that disproportionation is often involved. The presence of sulphide oxidizing bacteria, benthic fauna and rooted macrophytes may substantially enhance oxic reoxidation. Deposition of sulphur is generally higher in eutrophic than in oligotrophic lakes because of a number of factors: a higher rate of sulphate reduction, enhanced sedimentation of organic sulphur and less reoxidation as a result of reduced penetration of oxygen into the sediments, a lack of faunal activity and rooted macrophytes.     

Physiological analysis of mutants of Saccharomyces cerevisiae impaired in sulphate assimilation.

The assimilation of sulphate in Saccharomyces cerevisiae, comprising the reduction of sulphate to sulphide and the incorporation of the sulphur atom into a four-carbon chain, requires the integrity of 13 different genes. To date, the functions of nine of these genes are still not clearly established. A set of strains, each bearing a mutation in one MET gene, was studied. Phenotypic studies and enzyme determinations showed that the products of at least five genes are needed for the synthesis of an enzymically active sulphite reductase. These genes are MET1, MET5, MET8, MET10 and MET20. Wild-type strains of S. cerevisiae can use organic metabolites such as homocysteine, cysteine, methionine and S-adenosylmethionine as sulphur sources. They are also able to use inorganic sulphur sources such as sulphate, sulphite, sulphide or thiosulphate. Here we show that both of the two sulphur atoms of thiosulphate are used by S. cerevisiae. Thiosulphate is cleaved into sulphite and sulphide prior to utilization by the sulphate assimilation pathway, as the metabolism of one sulphur atom from thiosulphate requires the presence of an active sulphite reductase.     

Sulphide formation and chemical composition of bottom sediments of some Italian lakes

Studies of sulphate reduction and rates of sulphide formation were made in the bottom sediments of the alpine lakes Lago Maggiore and Lago Lugano. The stock of sulphide sulphur was found to be 500–1500 mg/l. The rate of sulphate reduction was 1–10 mg S/l/day. Total numbers of bacteria in sediments varied from 0,5 to 5.10⁹ cells/cm³ of wet mud. Chemical analyses of the carbon, nitrogen and phosphorus were also made. The possible influence of pollution on the sulphur cycle in these lakes is discussed.     

Efficacy and phytotoxicity of lime sulphur in organic apple production

Curative and preventive efficacy and phytotoxicity of lime sulphur spray schedules, based on a warning system, were evaluated in the Netherlands during two growing seasons under field conditions. In most cases, lime sulphur treatments applied either curatively or preventively resulted in significantly lower scab damage on both the leaves and fruits compared to wettable sulphur treatments. However, all lime sulphur treatments showed high phytotoxicity values, reduced leaf size and had a tendency to a reduced yield quality compared to all other treatments. For curative schedules of lime sulphur on scab control, phytotoxicity and yield did not differ significantly from preventive schedules of lime sulphur. However, the use of a warning system combined with curative schedules of lime sulphur saved one and two lime sulphur sprays in 2000 and 2001, respectively, compared to the preventive treatments of lime sulphur. Our results demonstrated that a curative spray programme with lime sulphur at 0.75–2%, applied 35–45 h after predicted infection periods, can provide effective primary apple scab control, but no benefit in either yield or fruit quality was reached under organic growing conditions. Moreover, research herein clearly showed that organic growers are forced to find a balance between good efficacy and phytotoxic effects of lime sulphur.     

Sulphur and nitrogen changes in forest soils of East Africa

Summary Sulphur measurements made on soils in East Africa revealed the unexpected occurrence of sulphates in forest subsoils. Soil profiles from plantation and natural forests were analysed and a general pattern of sulphur distribution was found.It has been found that in addition to the sulphur cycle dependent upon microbiological oxidation of organic sulphur there exists a cycle whereby sulphate is circulated as such between trees and soil.The biological oxidation of organic sulphur in the soil is an extremely slow process compared with that of carbon and nitrogen. Treatment with calcium carbonate, nitrates and non-sulphur-containing amino acids had no effect upon the subsequent sulphate production. Incubation with either S-containing amino acids or with calcium sulphate however, resulted in an increased rate of soil-sulphur oxidation and this effect is being further investigated.An aqueous extract of wattle leaves proved to inhibit nitrification in the soil for short periods and evidence is presented which suggests that methionine may be involved in this effect.     

The genus thiobacillus: Physiology and industrial applications

This review deals with different aspects concerning the genus Thiobacillus as an obligat chemoautotroph able to oxidize reduced anorganic sulphur compounds. There are given the following topics: physiology of the genus (nutritional requirements, enzymatic complexes for sulphur oxidation, energy generation, reductive CO₂ assimilation and growing in presence of organic compounds). The ecological significance of Thiobacilli in the sulphur cycle in Nature is presented. The industrial applications of Thiobacilli in respect to the leaching processes that allow the recovery of metals through oxidation and solubilization from low-grade ores are discussed, with special reference to copper and uranium. A critical revision is done of acid mine drainage impact on the environment, and the use of adequate countermeasures is stressed.     

The distribution of sulphur in the muds,water and vegetation of Lake Victoria

Summary The sulphur contents of the muds, water and vegetation at the northern end of Lake Victoria have been determined. Contrary to previous assumptions it was found that the sulphur in the bottom deposits is principally in the form of organic compounds and not as sulphides. Evidence is presented which suggests that the muds are in an aerated condition. The water of the lake contains extremely small amounts of sulphur and receives a negligible quantity of this element from the rain. The soils of the islands in the lake are rocky and well-leached of sulphur except where patches of forest conserve it. Certain peculiarities were noted in the behaviour of the muds and these are to be discussed in a future paper.     

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.     

Incubation studies on mineralization of organic sulphur and organic nitrogen

Summary Incubation studies were carried out to investigate the release of sulphur and nitrogen in West Indian soils. Sulphur and nitrogen released or fixed were estimated at 10 days intervals up to 60 days incubation period.All the soils released sulphate when incubated at 30°C. A rapid initial flush of mineralization of both sulphur and nitrogen took place in Cocal fine sand and Montreal sandy loam. In Piarco sandy clay loam and Mayaro sandy loam sulphur mineralization was not accompanied by a concomitant mineralization of nitrogen. An inconsistent pattern of release of sulphur and nitrogen was noticed in Montserrat clay, Akers sandy clay loam, Bellevue sandy clay loam and Soufriere cindery gravelly loamy sand.The release of sulphur does not appear to be related to the total amount of carbon, nitrogen or sulphur. Nitrogen mineralized was significantly correlated with total nitrogen and total sulphur. The correlation between organic matter and nitrogen mineralized was highly significant (r=0.87^**) whereas with sulphur mineralized it did not reach significance. This suggests that nitrogen and sulphur are not mineralized at the same rate in these soils.     

Palaeolimnological studies of laminated sediments from the Shropshire-Cheshire meres

Studies of frozen and soft mud cores from Ellesmere Mere, Rostherne Mere and Berrington Pool, the three deepest of the Shropshire-Cheshire meres of the English Midlands, reveal the presence of laminations which may be varves. This hypothesis is being tested by means of fine resolution diatom and other microfossil analysis after the method of Simola (1977). Even where the laminations are faint and disrupted, it appears that seasonal signals from algal blooms are preserved.Organic geochemical analyses of sediments from Ellesmere show that the uppermost layers contain abundant organic matter (over 17% total dry matter) and that the extractable lipid fractions from different horizons exhibit clear compositional differences. These are produced by temporal changes in the organic inputs to the sediments, and also by diagnetic effects.The clastic and organic content of the cores also provides evidence for lake level variations in this area over the last 250 years.     

Biodesulphurization of mengen lignite by Rhodoccocus rhodochrous in a batch stirred and aerated tank fermenter

The biodesulphurization of Mengen lignite by a mesophilic bacterium, Rhodococcus rhodochrus ATCC 53968, was investigated in a batch stirred and aerated reactor. The experiments were carried out at 28°C with an inoculum percentage, initial pH, initial sodium acetate and lignite concentration of the biodesulphurization medium of 8% [v/v], 6.5 mM, 20 mM and 20 g/l, respectively. Variations in the sulphur contents of the lignite relative to the biodesulphurization period were monitored. The effects of the stirring and aeration rates on the removal of different sulphur forms from coal were investigated in the ranges 450–1,200 rpm and 0.1–0.53 vvm and the optimum values were found to be 500 rpm and 0.18 vvm, respectively. An increase in the total sulphur reduction with increasing biodesulphurization time was observed. The maximum total sulphur removal percentage was found to be 15.2% at 1,200 rpm after four days of incubation. The highest total sulphur removal rate was calculated on the second day of microbial desulphurization for each run. The total and organic sulphur contents of the coal after biodesulphurization were correlated with the stirring and aeration rates by using the non-linear least squares regression method. In the experimental runs lasting 8 days, the highest organic sulphur reducing percentage of 10.1% was obtained at a stirring rate of 500 rpm and an aeration rate of 0.40 vvm.     

The Uptake and Metabolism of Sulphate in Scenedesmus as Influenced by Citrate, Carbon Dioxide, and Metabolic Inhibitors

The incorporation of sulphur from external sulphate into different fractions was studied in cells with a P content of 0.6 to 1 mg/g fresh weight as against 3 to 5 mg/g fresh weight in normal cells. — There is a flat and broad optimum for the action of pH in the region between 5.7 and 7. — In most cases, citrate inhibits the uptake of sulphur. — Five per cent CO₂ in the air enhances the incorporation of S. It is suggested that the effects of CO₂ may well be exerted by way of the carboxylation and decarboxylation mechanisms in the cells. — Selenate inhibits the formation of DNA-S and protein S more than that of lipid S, but the main effect in both cases seems to be in an early step of the assimilation of sulphate. In the absence of external phosphate, the inhibition is counteracted by CO₂, especially in darkness. Phosphate enhances the action of selenate on the organic S fractions, and in its presence CO₂ and darkness make the inhibition more pronounced. — Without P in the medium, the effects of selenate on uptake into the inorganic sulphate fraction are smaller than when the organic fractions are concerned. In the presence of CO₂ even stimulations due to selenate have been observed. External phosphate brings the inhibition of uptake into cellular SO₄^2- to the same level as found in the case of organic S. More than one pathway for the uptake as SO₄^2-seem possible. — Anaerobiosis and menadione affect the organic S fractions more than the sulphate; 2,4-dinitrophenol has a more uniform action all over the field.     

HMSS2: An advanced tool for the analysis of sulphur metabolism,including organosulphur compound transformation,in genome and metagenome assemblies

The global sulphur cycle has implications for human health, climate change, biogeochemistry and bioremediation. The organosulphur compounds that participate in this cycle not only represent a vast reservoir of sulphur but are also used by prokaryotes as sources of energy and/or carbon. Closely linked to the inorganic sulphur cycle, it involves the interaction of prokaryotes, eukaryotes and chemical processes. However, ecological and evolutionary studies of the conversion of organic sulphur compounds are hampered by the poor conservation of the relevant pathways and their variation even within strains of the same species. In addition, several proteins involved in the conversion of sulphonated compounds are related to proteins involved in sulphur dissimilation or turnover of other compounds. Therefore, the enzymes involved in the metabolism of organic sulphur compounds are usually not correctly annotated in public databases. To address this challenge, we have developed HMSS2, a profiled Hidden Markov Model-based tool for rapid annotation and synteny analysis of organic and inorganic sulphur cycle proteins in prokaryotic genomes. Compared to its previous version (HMS-S-S), HMSS2 includes several new features. HMM-based annotation is now supported by nonhomology criteria and covers the metabolic pathways of important organosulphur compounds, including dimethylsulphoniopropionate, taurine, isethionate, and sulphoquinovose. In addition, the calculation speed has been increased by a factor of four and the available output formats have been extended to include iTol compatible data sets, and customized sequence FASTA files.     

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.     

Distribution and growth of benthic macroinvertebrates among different patch types of the littoral zones of two arctic lakes

1. To evaluate the effect of habitat patch heterogeneity on abundance and growth of macroinvertebrates in arctic lakes, macroinvertebrate abundance, individual biomass, and potential food resources were studied in three patch types in two arctic lakes on the Alaskan North Slope near the Toolik Lake Field Station. An experiment was conducted to determine which sediment patch type supported higher growth rates for Chironomus sp., a commonly occurring macroinvertebrate. 2. Potential organic matter (OM) resources were significantly higher in both rock and macrophyte patches than in open‐mud patches. Total macroinvertebrate densities in both lakes were highest in rock patches, intermediate in macrophytes and lowest in open‐mud. The open‐mud patches also had lower species richness compared with other patch types. Additionally, individual biomass for one clam species and two chironomid species was significantly greater in rock patches than in open‐mud. 3. In a laboratory experiment, Chironomus showed two to three times greater mass increase in sediments from macrophyte and rock patches than from open‐mud patches. Rock and macrophyte experimental sediments had at least 1.5 × the percentage OM as open‐mud sediments. 4. Chlorophyll a appeared to be the best predictor for invertebrate abundances across all patch types measured, whereas OM content appeared to be the variable most closely associated with Chironomus growth. 5. Our results combined with previous studies show that the relationships between macroinvertebrate community structure, individual growth, and habitat heterogeneity are complex, reflecting the interaction of multiple resources, and biotic interactions, such as the presence or absence of a selective vertebrate predator (lake trout, Salvelinus namaycush).     

The bacteria of the sulphur cycle

This paper concentrates on the bacteria involved in the reductions and oxidations of inorganic sulphur compounds under anaerobic conditions. The genera of the dissimilatory sulphate-reducing bacteria known today are discussed with respect to their different capacities to decompose and oxidize various products of fermentative degradations of organic matter. The utilization of molecular hydrogen and formate by sulphate reducers shifts fermentations towards the energetically more favourable formation of acetate. Since acetate amounts to about two-thirds of the degradation products of organic matter, the complete anaerobic oxidation of acetate by several genera of the sulphate-reducing bacteria is an important function for terminal oxidation in sulphate-sufficient environments. The results of pure culture studies agree well with ecological investigations of several authors who showed the significance of sulphate reduction for the complete oxidation of organic matter in anaerobic marine habitats. In the dissimilatory sulphur-reducing bacteria of the genus Desulfuromonas the oxidation of acetate is linked to the reduction of elemental sulphur. Major characteristics of the anaerobic, sulphide-oxidizing phototrophic green and purple sulphur bacteria as well as of some facultative anoxygenic cyanobacteria, are given. By the formation of elemental sulphur and sulphate, these bacteria establish sulphur cycles with the sulphide-forming bacteria. In view of the morphological diversity of the sulphate-reducing bacteria and question of possible evolutionary relations to phototrophic sulphur bacteria is raised.