Degradation of dibenzothiophene by Pseudomonas putida

The microbial degradation of dibenzothiophene (DBT) and other organosulphur compounds such as thiophene-2-carboxylate (T2C) is of interest for the potential desulphurization of coal. The feasibility of degradation of DBT and T2C by Pseudomonas putida and other bacteria was analysed. Pseudomonas putida oxidized sulphur from DBT in the presence of yeast extract, but it did not when DBT was the sole source of carbon.     

Desulphurization of dibenzothiophene and diesel oils by bacteria

AIMS: To study the desulphurization of dibenzothiophene (DBT), a recalcitrant thiophenic component of fossil fuels, by two bacteria namely Rhodococcus sp. and Arthrobacter sulfureus isolated from oil-contaminated soil/sludge in order to use them for reducing the sulphur content of diesel oil in compliance with environmental regulations. METHODS AND RESULTS: The desulphurization pathway of DBT by the two bacteria was determined by gas chromatography (GC) and GC-mass spectrometry. Both organisms were found to produce 2-hydroxy biphenyl (2-HBP), the desulphurized product of DBT. Sulphur contents of culture supernatants of Rhodococcus sp. and A. sulfureus grown with DBT as sole sulphur source were analysed by X-ray fluorescence indicating sulphur levels of 8 and 10 ppm, respectively, as compared with 27 ppm in control. In order to study desulphurization of diesel oils obtained from an oil refinery, resting cell studies were carried out which showed a decrease of about 50% in sulphur content of the oil obtained from the hydrodesulphurization (HDS) unit of the refinery. CONCLUSIONS: Rhodococcus sp. and A. sulfureus selectively remove sulphur from DBT to form 2-HBP. Application of these bacteria for desulphurization of diesel showed promising potential for decreasing the sulphur content of diesel oil. SIGNIFICANCE AND IMPACT OF THE STUDY: The process of microbial desulphurization described herein can be used for significantly reducing the sulphur content of oil, particularly, after the process of HDS which would help in meeting the regulatory standards for sulphur level in diesel oil.     

Microbial removal of pyrite from coal using a percolation bioreactor

Summary To compare the suspension and the percolation process system for the microbial desulphurization of coal the microbial pyrite oxidation in coal during storage in dumps was investigated in laboratory experiments with Thiobacillus ferrooxidans using a percolation bioreactor and resulted in a removal of 75% of pyrite within 70 days. In the initial desulphurization phase 450 mg pyritic-S/kg coal per day were oxidized at maximum rate, while the overall rate was determined to 130 mg pyritic-S/kg coal per day. During the desulphurization the mean particle size of the coal was reduced from 0.55 mm to 0.175 mm. As shown by microscopy and elemental analyses of the coal the pyrite was completely removed from small coal particles, whereas parts of it remained in the core of the greater particles.     

Idle time in the washing and iron concentration in leachate removed: two basic parameters in the desulphurization of coal in a packed column

Column biodesulphurization of coal is at the experimental stage and is influenced by many variables including temperature, pH, particle size, concentration of iron in solution, among others. Idle time in the washing process and the concentration of dissolved iron in the purged leachate are two variables with a definite effect on the yield of the desulphurization system. In the laboratory, several trials were run with columns packed with coal for different idle times: 1, 2, 3, 5, 6 and 7 days, and for different concentrations of iron in the purged leachate: 500 to 4,000 mg/l. The optimal values for the two variables; that is, those allowing for the highest desulphurization yields, were idle times of 3 and 5 days, which give an elimination of 56% and 49% of pyritic sulphur, respectively, and 3,000 mg/l of iron concentration in the purged leachate, giving a decrease in pyritic sulphur in coal of 57%.     

Bioremoval of organic and inorganic sulphur from coal samples

The microbial ecology of different Spanish coal samples has been studied. Several bacteria have been isolated from enrichment cultures and characterised and their biodesulphurization abilities evaluated. Using morphological and physiological properties, different isolates have been related to species of the Xanthomonas, Pseudomonas, Chryseomonas and Moraxella genera. Some of the isolates, B(30)15 and T(30)10, gave important levels of organic desulphurization, close to 70%. Other isolates, B(30)7 and B(30)8, were able to remove inorganic sulphur with high efficiencies, over 67%. One of the isolates, B(30)10, metabolically related to Xanthomonas maltophila, was able to remove both organic and inorganic sulphur at neutral pH, with efficiencies of 69% and 68% respectively. The results obtained underline the potential use of some of these strains for industrial coal desulphurization processes. Received: 26 June 1998 / Received revised: 1 October 1998 / Accepted: 2 October 1998     

Oxidation of dibenzothiophene (DBT) by Serratia marcescens UCP 1549 formed biphenyl as final product

ABSTRACT: BACKGROUND: The desulphurization of dibenzothiophene (DBT), a recalcitrant thiophenic fossil fuel component by Serratia marcescens (UCP 1549) in order for reducing the sulphur content was investigated. The study was carried out establishing the growth profile using Luria Bertani medium to different concentrations of DBT during 120hours at 28oC, and orbital shaker at 150rpm. RESULTS: The results indicated that concentrations of DBT 0.5, 1.0 and 2.0 mM do not affected the growth of the bacterium. The DBT showed similar Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MCB) (3.68 mM). The desulphurization of DBT by S. marcescens was used with 96 hours of growth on 2mM of DBT, and was determined by gas chromatography (GC) and GC-mass spectrometry. In order to study the desulphurization process by S. marcescens was observed the presence of a sulfur-free product at 16 hours of cultivation The results show that S. marcescens oxidizes DBT to its corresponding DBT-5 oxide and then to DBT-sulfone, without the formation of any biphenyl. CONCLUSIONS: The data suggests the use of metabolic pathway "4S" by S. marcescens (UCP 1549) and formed biphenyl. The microbial desulphurization process by S. Serratia can be suggest significant reducing sulphur content in DBT, and showed promising potential for reduction of the sulfur content in diesel oil.     

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.     

Mikrobiologische Kohleentschwefelung

SO₂emissions arising by burning of coal represent an important ecological problem. Therefore, in international scale it is worked today in the development of techniques for solving this problem. A possibility consists in the microbial conversion of sulphur compounds of coal before its burning into compounds which not produce SO₂ by burning. Sulphur is bound in inorganic and organic form in coal. The composition may strongly differ in dependence on the kind of coal and its deposit. For the bioconversion of different sulphur compounds specific microorganisms were used. The paper gives an overview about the situation and the tendencies of the research in this field and also some informations of our own research.     

Microbial desulphurization of heavy oils and bitumen

Most oil producing countries have extensive reserves of heavy oil and bitumen. As easily accessible sources of conventional crudes decline, these reserves will become more important in supplementing the energy requirements. Heavy oil and bitumen are highly viscous and contain 3 to 6% sulphur. These objectionable quantities of sulphur must be removed before being acceptable as refinery feedstock. This paper addresses the potential of biological desulphurization of heavy oil and bitumen. The aerobic and anaerobic processes to remove organic as well as inorganic sulphur have been reviewed. To date, most studies were performed with model substrates, particularly dibenzothiophene (DBT) in a synthetic medium. Early work concerned with the isolation of microorganisms, identification and characterization of intermediate metabolites, and the development of growth media. No commercially viable process has emerged since the engineering details of the process have not been addressed conclusively. Due to high utility and catalyst cost conventional hydrodesulphurization processes are reported to be uneconomic in case of high sulphur oils. Microbial desulphurization, on the other hand, appears to be promising due to the inherent low energy requirement. This process may become more attractive by the application of genetically modified bacteria and improvements in bioreactor design.     

Microbial coal desulphurization: calculation of costs

The sulphur found in coal is either part of the molecular structure, is contained in minerals such as pyrite (FeS₂), or occurs in minor quantities in the form of sulfate. When pyrite crystals are finely distributed within the coal matrix, mechanical cleaning can only remove part of the pyrite. It can, however, be removed by microbial action requiring only mild reaction conditions. The process involves simple equipment, almost no chemicals, but relatively long reaction times and, eventually, disposal of dissolved iron sulfate. Investment and operating costs are estimated for different process configurations on an industrial scale.     

Analysis of low-molecular mass products from biosolubilized coal

Abstract A relatively simple, rapid sample preparation method has been developed for analysis of low-molecular mass compounds present in soluble coal products generated by microbial coal solubilizing agents. Acidification of the sample followed by direct extraction into hexanes is coupled with gas chromatography/mass spectrometry analysis for characterization of the soluble coal products. Characterization of the products can contribute to a more complete understanding of the solubilization processes involved, provide further information as to the structure of coal and identify products of potential commercial value.     

The role of soil microbes in plant sulphur nutrition

Chemical and spectroscopic studies have shown that in agricultural soils most of the soil sulphur (>95%) is present as sulphate esters or as carbon-bonded sulphur (sulphonates or amino acid sulphur), rather than inorganic sulphate. Plant sulphur nutrition depends primarily on the uptake of inorganic sulphate. However, recent research has demonstrated that the sulphate ester and sulphonate-pools of soil sulphur are also plant-bioavailable, probably due to interconversion of carbon-bonded sulphur and sulphate ester-sulphur to inorganic sulphate by soil microbes. In addition to this mineralization of bound forms of sulphur, soil microbes are also responsible for the rapid immobilization of sulphate, first to sulphate esters and subsequently to carbon-bound sulphur. The rate of sulphur cycling depends on the microbial community present, and on its metabolic activity, though it is not yet known if specific microbial species or genera control this process. The genes involved in the mobilization of sulphonate- and sulphate ester-sulphur by one common rhizosphere bacterium, Pseudomonas putida, have been investigated. Mutants of this species that are unable to transform sulphate esters show reduced survival in the soil, indicating that sulphate esters are important for bacterial S-nutrition in this environment. P. putida S-313 mutants that cannot metabolize sulphonate-sulphur do not promote the growth of tomato plants as the wild-type strain does, suggesting that the ability to mobilize bound sulphur for plant nutrition is an important role of this species.     

Preliminary Evidence for a Sulphur Cycle in Movile Cave,Romania

In order to investigate the food chain and energy balance of the chemolithoautotrophically‐based ecosystem of the sulphur spring in Movile Cave as a model system for extraterrestrial life, a first sampling campaign was done. Microbial diversity and activity were analysed by MPN‐enumeration methods and microcalorimetry, respectively. In addition, a speciation of the inorganic sulphur compounds by HPLC and IC techniques was performed. Metabolic activities were predominantly connected with thick microbial mats floating on the water surface of the cave. These mats showed an aerobic heat evolution of about 1200 μW/g and contained about 500 μmol/g elemental sulphur. In contrast, other samples collected from cave water, sediment and rock exhibited only activities of maximal 40 to 60 μW/g and contained only up to 2.5 μmol/g elemental sulphur. As the main primary producers aerobic and facultatively anaerobic sulphur oxidisers were identified at high numbers, occasionally exceeding 10⁷ CFU/g. Methylotrophic bacteria were present in all samples at up to 10⁶ CFU/g, indicating the important role of C1 metabolism for the cave ecosystem. Although reduced sulphur species were biologically oxidised to sulphuric acid, the pH values of the samples ranged from 6.5 to 8.2 due to the high buffering capacity of the cave walls, which consisted mainly of limestone. Surprisingly, not only neutrophilic but also extremely acidophilic bacteria were detected. Sulphate reducers were present in both aerobic and anaerobic zones. The data presented suggest a close interdependence of sulphur oxidation and reduction as well as carbon dioxide and other C1 compound metabolism in the most biologically active zone of the cave ecosystem, i.e. the floating microbial mats.     

Manipulation of the DNA coding for the desulphurizing activity in a new isolate of Arthrobacter sp.

A new bacterial strain able to cleave CS bonds from organosulphur heterocyclic compounds through the 4-S pathway and tentatively classified as Arthrobacter sp. was recently isolated. In the present short article we describe the cloning and the characterization of the DNA encoding the enzymes responsible for desulphurization in this microorganism, referred to as Arthrobacter sp. DS7. The desulphurization operon was found to be located in a large plasmid that also bears the genes conferring cadmium and arsenic resistance. By shortening this plasmid, a new cloning vector was prepared and used to obtain a recombinant derivative strain that desulphurizes dibenzothiophene despite of the presence of inorganic sulphur in the growth medium. Received: 25 May 1998 / Received revision: 4 September 1998 / Accepted: 13 September 1998     

Microbial methods for desulfurization of coal

As a result of acid rain problems, desulfurization of coal has been given increasing attention in recent years. Microbial methods of coal desulfurization have significant advantages over chemical and physical methods. New methods and organisms have been developed for microbial desulfurization of coal in recent years. This article summarizes microbial processes and properties of the organisms used in coal desulfurization.     

Coal methanogenesis: a review of the need of complex microbial consortia and culture conditions for the effective bioconversion of coal into methane

Microbial biodegradation of coal into low-molecular-weight compounds such as methane has been extensively researched in the last two decades because of the underlying environmental and industrial applications of this technique as compared to the chemical and physical methods of coal conversions. However, the irregular structure of coal and the need for complex microbial consortia under specific culture conditions do not make this biotransformation an ideal process for the development of anaerobic bioreactors. The most abundant species in a methanogenic culture are acetoclastic and hydrogenotrophic methanogens which utilize acetate and H₂+CO₂, respectively. Medium- to low-rank coals such as high-volatile bituminous, sub-bituminous and lignite are more promising in this bioconversion as compared to semi- and meta-anthracite coals. While covering the details of the ideal culture conditions, this review enlightens the need of research setups to explore the complex microbial consortia and culture conditions for maximum methane production through coal methanogenesis.     

Decolorization of Pulp-Paper Mill Effluents by White-Rot Fungi

ABSTRACT:?

Phenolic effluents are waste products of pulp and paper, coal conversion, dying, textile, and olive oil industries. Such effluents impose coloration and toxicity problems in the receiving waters, causing serious environmental hazards. The pulp and paper mill effluent is highly colored, imparting black/brown color to the water body. The color is mainly due to lignin and its derivatives released during various stages in the paper-making process. The complex nature of such lignin compounds and their phenolic nature make them extremely resistant to microbial degradation. Conventional treatment methods such as aerated lagoons and activated sludge process are ineffective in removing color. However, physical and chemical treatment methods, including ultrafiltration, ion-exchange, and lime precipitation, are expensive and less efficient. Therefore, alternate low-cost biotreatment processes are now being considered, most of which are based on lignin-degrading fungi. Depending on the treatment process, the fungal inoculum for decolorization could be used in the form of mycelium, pellets, or in the immobilized state. The decomposition of lignin is an enzymatic process employing various ligninases being produced by the fungal species. Soluble and immobilized ligninolytic enzymes have also been employed for effluent decolorization. Therefore, the present review is an attempt to compile the scattered information on pulp-paper mill effluent decolorization employing microbes. The structure, distribution, physiology, and enzymology of lignin degradation is also briefly discussed.     

Isolation and characterization of oil-desulphurizing bacteria

The objective of this study was to isolate local bacterial strains capable of removing sulphur from oil fractions without degrading the hydrocarbon. Oil biodesulphurization is an important step in combating pollution problems emanating from burning fossil fuels. Organisms which survive on oil are plentiful in local Kuwaiti soils; however, those that selectively only attack the carbon–sulphur bond are more difficult to find. Three strains were isolated based on their ability to use dibenzothiophene (DBT) as a sole source of sulphur for growth at 30 °C. Similar to other biodesulphurization organisms, the strains convert DBT to [2-hydroxybiphenyl (2-HBP) as detected by gas chromatography (GC). The specific desulphurization activity was in the range 5–13 mol 2-HBP/g-cell × h. Identification of the strains, based on 16 rRNA gene sequence similarity, showed the strains to be Rhodococcus erythropolis and Rhodococcus globerulus. The biodesulphurization activity was enhanced by promoting oxidore-ductase enzyme co-expression through the addition of a carbon source. The desulphurization was limited by the availability of DBT to the organism. Interfacial mass transfer through the aqueous-organic layer was confirmed to be a limiting factor.     

Sulphide oxidation to elemental sulphur in a membrane bioreactor: performance and characterization of the selected microbial sulphur-oxidizing community

In leather tanning industrial areas sulphide management represents a major problem. However, biological sulphide oxidation to sulphur represents a convenient solution to this problem. Elemental sulphur is easy to separate and the process is highly efficient in terms of energy consumption and effluent quality. As the oxidation process is performed by specialized bacteria, selection of an appropriate microbial community is fundamental for obtaining a good yield. Sulphur oxidizing bacteria (SOB) represent a wide-ranging and highly diversified group of microorganisms with the capability of oxidizing reduced sulphur compounds. Therefore, it is useful to select new microbes that are able to perform this process efficiently. For this purpose, an experimental membrane bioreactor for sulphide oxidation was set up, and the selected microbial community was characterized by constructing 16S rRNA gene libraries and subsequent screening of clones. Fluorescence in situ hybridization (FISH) was then used to assess the relative abundance of different bacterial groups. Sulphide oxidation to elemental sulphur proceeded in an efficient (up to 79% conversion) and stable way in the bioreactor. Both analysis of clone libraries and FISH experiments revealed that the dominant operational taxonomic unit (OTU) in the bioreactor was constituted by Gammaproteobacteria belonging to the Halothiobacillaceae family. FISH performed with the specifically designed probe tios_434 demonstrated that this OTU constituted 90.6+/-1.3% of the bacterial community. Smaller fractions were represented by bacteria belonging to the classes Betaproteobacteria, Alphaproteobacteria, Deltaproteobacteria, Clostridia, Mollicutes, Sphingobacteria, Bacteroidetes and Chlorobia. Phylogenetic analysis revealed that clone sequences from the dominant OTU formed a stable clade (here called the TIOS44 cluster), within the Halothiobacillaceae family, with sequences from many organisms that have not yet been validly described. The data indicated that bacteria belonging to the TIOS44 cluster were responsible for the oxidation process.