Mineralization of S from dibenzothiophene, dibenzothiophene sulphone, and benzene sulphonic acid by soil isolates

The presence of substantial levels of organic S in coal is a major source of air pollution, and considerable efforts are being made to devise a cost-effective way of removing this form of sulphur. One method is to develop naturally occurring bacteria capable of heterocyclic organic S degradation and S mineralization. In this study, fourteen isolates capable of dibenzothiophene (DBT), dibenzothiophene sulphone (DBTS) or benzene sulphonic acid (BSA) decomposition were obtained from samples collected from an abandoned strip mine. The degradation of DBT varied from 4.4 to 91% and the mineralization of S as sulphate was less than or equal to 1.5%. Higher rates of DBTS decomposition were determined (94.9 to 97.7%) and S mineralization varied from 21.8 to 30.8%. The extent of BSA degradation could not be determined, but 57.8 to 71.1% of the S was mineralized as sulphate. All of the soil isolates possessed a single plasmid 20 to 23 kb in size.     

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.     

Expression of dibenzothiophene-degradative genes in two Pseudomonas species

The genes encoding dibenzothiophene (DBT) degradation in Pseudomonas alcaligenes strain DBT2 were cloned into plasmid pC1 by other workers. This plasmid was conjugally transferred into a spontaneous variant of Pseudomonas sp. HL7b (designated HL7bR) incapable of oxidizing DBT (Dbt- phenotype). Acquisition of plasmid pC1 simultaneously restored oxidation of DBT and naphthalene to the transconjugant, although the primary DBT metabolite produced by transconjugant HL7bR(pC1) corresponded to that produced by wild-type strain DBT2 rather than that from wild-type strain HL7b. Inducers of the naphthalene pathway (naphthalene, salicylic acid, and 2-aminobenzoate) stimulated DBT oxidation in transconjugant HL7bR(pC1) when present at 0.1 mM concentrations but had no effect on wild-type strain HL7b. Higher concentrations (5 mM) of salicylic acid and naphthalene were inhibitory to DBT oxidation in all strains. DNA-DNA hybridization was not observed between plasmid pC1 and genomic DNA from strains HL7b or HL7bR, nor between authentic naphthalene-degradative genes (plasmid NAH2) and either plasmid pC1 or strain HL7b, despite the observation that the degradative genes encoded on plasmid pC1 functionally resembled broad-specificity naphthalene-degradative genes. Transconjugant HL7bR(pC1) is a mosaic of the parental types regarding DBT metabolite production, regulation, and use of carbon sources.     

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.     

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.     

Plasmid-mediated degradation of dibenzothiophene by Pseudomonas species

The microbial transformation of dibenzothiophene (DBT) is of interest in the potential desulfurization of oil. We isolated three soil Pseudomonas species which oxidized DBT to characteristic water-soluble, sulfur-containing products. Two of our isolates harbored a 55-megadalton plasmid; growth in the presence of novobiocin resulted in both loss of the plasmid and loss of the ability to oxidize DBT. Reintroduction of the plasmid restored the ability to oxidize DBT to water-soluble products. The products resulting from the oxidation of DBT were characterized and included 3-hydroxy-2-formyl benzothiophene, 3-oxo-[3'-hydroxy-thionaphthenyl-(2)-methylene]-dihydrothionaph thene, and the hemiacetal and trans forms of 4-[2-(3-hydroxy)-thianaphthenyl]-2-oxo-3-butenoic acid. The products of DBT oxidation were inhibitory to cell growth and further DBT oxidation. DBT oxidation in our soil isolates was induced by naphthalene or salicylate and to a much lesser extent by DBT and was repressed by succinate.     

Plasmid-mediated degradation of dibenzothiophene by Pseudomonas species.

The microbial transformation of dibenzothiophene (DBT) is of interest in the potential desulfurization of oil. We isolated three soil Pseudomonas species which oxidized DBT to characteristic water-soluble, sulfur-containing products. Two of our isolates harbored a 55-megadalton plasmid; growth in the presence of novobiocin resulted in both loss of the plasmid and loss of the ability to oxidize DBT. Reintroduction of the plasmid restored the ability to oxidize DBT to water-soluble products. The products resulting from the oxidation of DBT were characterized and included 3-hydroxy-2-formyl benzothiophene, 3-oxo-[3'-hydroxy-thionaphthenyl-(2)-methylene]-dihydrothionaph thene, and the hemiacetal and trans forms of 4-[2-(3-hydroxy)-thianaphthenyl]-2-oxo-3-butenoic acid. The products of DBT oxidation were inhibitory to cell growth and further DBT oxidation. DBT oxidation in our soil isolates was induced by naphthalene or salicylate and to a much lesser extent by DBT and was repressed by succinate.     

Desulfurization of dibenzothiophene by Corynebacterium sp. strain SY1.

Strain SY1, identified as a Corynebacterium sp., was isolated on the basis of the ability to utilize dibenzothiophene (DBT) as a sole source of sulfur. Strain SY1 could utilize a wide range of organic and inorganic sulfur compounds, such as DBT sulfone, dimethyl sulfide, dimethyl sulfoxide, dimethyl sulfone, CS2, FeS2, and even elemental sulfur. Strain SY1 metabolized DBT to dibenzothiophene-5-oxide, DBT sulfone, and 2-hydroxybiphenyl, which was subsequently nitrated to produce at least two different hydroxynitrobiphenyls during cultivation. These metabolites were separated by silica gel column chromatography and identified by nuclear magnetic resonance, UV, and mass spectral techniques. Resting cells of SY1 desulfurized toluenesulfonic acid and released sulfite anion. On the basis of these results, a new DBT degradation pathway is proposed.     

Dibenzothiophene Biodegradation by a Pseudomonas sp. in Model Solutions

The presence of a fatty acid and an n-alkane may affect the biodegradation rate of aromatic sulphur compounds such as dibenzothiophene (DBT). A fatty acid (hexadecanoic acid) may form micellar structures favouring DBT bioavailability. n-Alkanes, such as n-dodecane or n-hexadecane, form a film around the aromatic sulphur molecule as a consequence of solvation, thus increasing DBT bioavailability. The mass-transfer rate from the solid to the aqueous phase controls the DBT biodegradation rate when DBT is the only carbon source. Diffusional coassimilation and microbial hydrophobic effects are rate-limiting steps in DBT biodegradation in the presence of aliphatic compounds. Diffusion depends on the DBT concentration in n-alkane, while cometabolism is associated with different n-alkane biodegradation rates. Through the definition of biodesulphurization selectivity and biodesulphurization efficiency, our investigations have shown that a selective aerobic biodesulphurization process is possible by using an unselective biocatalyst, such as a Pseudomonas sp.     

Desulfurization of dibenzothiophene by Corynebacterium sp. strain SY1.

Strain SY1, identified as a Corynebacterium sp., was isolated on the basis of the ability to utilize dibenzothiophene (DBT) as a sole source of sulfur. Strain SY1 could utilize a wide range of organic and inorganic sulfur compounds, such as DBT sulfone, dimethyl sulfide, dimethyl sulfoxide, dimethyl sulfone, CS2, FeS2, and even elemental sulfur. Strain SY1 metabolized DBT to dibenzothiophene-5-oxide, DBT sulfone, and 2-hydroxybiphenyl, which was subsequently nitrated to produce at least two different hydroxynitrobiphenyls during cultivation. These metabolites were separated by silica gel column chromatography and identified by nuclear magnetic resonance, UV, and mass spectral techniques. Resting cells of SY1 desulfurized toluenesulfonic acid and released sulfite anion. On the basis of these results, a new DBT degradation pathway is proposed.     

Cloning and expressing DBT (dibenzothiophene) monooxygenase gene (dszC) from Rhodococcus sp. DS-3 in Escherichia coli

Dibenzothiophene (DBT) monooxygenase (DszC)catalysis,the first and also the key step in the microbial DBT desulfurization,is the conversion of DBT to DBT sulfone (DBTO2).In this study,dszC of a DBT-desulfiaizing bacterium Rhodococcus sp.DS-3 was cloned by PCR.The sequence cloned was 99% homologous to Rhodococcus erythropolis IGTS8 that was reported in the Genebank.The gene dszC could be overexpressed effectively after being inserted into plasmid pET28a and transformed into E.coli BL21 strain.The expression amount of DszC was about 20% of total supernatant at low temperature.The soluble DszC in the supematant was purified by Ni2+ chelating His-Tag resin column and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to electronics purity.Only one band was detected by Western-blotting,which is for the antibody released in mouse against purified DszC in the expression product of BL21 (DE3,paC5) and Rhodococcus sp.DS-3.The activity of purified DszC was 0.36 U.DszC can utilize the organic compound such as DBT and methyl-DBT,hut not DBT derivates such as DBF,which has no sulfur or inorganic sulfur.     

The distribution of sulphur in the mud of Lake Victoria

Summary Re-examination of mud from Lake Victoria showed the presence of pyrite. It has been claimed that these muds contain abnormally large amounts of organic sulphur, but pyritic and organic sulphur would not be distinguished by the method that was used. The organic sulphur content of the mud is therefore much less than previously reported, and there seems to be no reason to assume the presence of unusual organic sulphur compounds.     

Degradation of phenanthrene,methylphenanthrenes and dibenzothiophene by a Sphingomonas strain 2mpII

Strain Sphingomonassp. (2MPII), isolated from marine sediment, was able to utilize phenanthrene (P) or 2-methylphenanthrene (2MP) as the sole carbon source. However, 9-methylphenanthrene (9MP) and dibenzothiophene (DBT) were weakly degraded. The degradation rates of 9MP and DBT increased in the presence of 2MP, whilst the degradation rate of 2MP increased in the presence of 9MP. However, the presence of DBT inhibited the degradation of 2MP. DBT sulfone, a DBT metabolite, was not assimilated by the bacteria and its presence also decreased the degradation rate of 2MP.     

石油生物脱硫菌Pseudomonas stutzeri UP-1的筛选

以二苯并噻吩(DBT)为模型化合物,筛选到一株能有效降解DBT的菌株,根据其菌落的形态特征、生理生化特征和分子生物学鉴定方法,确定其为Pseudomonms stutzer UP1。该菌株对DBT具有较强的降解能力,降解终产物为水溶性物质。通过对降解产物的分析,初步推断DBT的降解符合Kodama机理。     

Selective Desulfurization of Dibenzothiophene by Rhodococcus erythropolis D-1

A dibenzothiophene (DBT)-degrading bacterium, Rhodococcus erythropolis D-1, which utilized DBT as a sole source of sulfur, was isolated from soil. DBT was metabolized to 2-hydroxybiphenyl (2-HBP) by the strain, and 2-HBP was almost stoichiometrically accumulated as the dead-end metabolite of DBT degradation. DBT degradation by this strain was shown to proceed as DBT → DBT sulfone → 2-HBP. DBT at an initial concentration of 0.125 mM was completely degraded within 2 days of cultivation. DBT at up to 2.2 mM was rapidly degraded by resting cells within only 150 min. It was thought this strain had a higher DBT-desulfurizing ability than other microorganisms reported previously.     

Combining co-culturing of Paenibacillus strains and Vitreoscilla hemoglobin expression as a strategy to improve biodesulfurization

Enhancement of the desulfurization activities of Paenibacillus strains 32O-W and 32O-Y were investigated using dibenzothiophene (DBT) and DBT sulfone (DBTS) as sources of sulphur in growth experiments. Strains 32O-W, 32O-Y and their co-culture (32O-W plus 32O-Y), and Vitreoscilla hemoglobin (VHb) expressing recombinant strain 32O-Yvgb and its co-culture with strain 32O-W were grown at varying concentrations (0·1–2 mmol l⁻¹) of DBT or DBTS for 96 h, and desulfurization measured by production of 2-hydroxybiphenyl (2-HBP) and disappearance of DBT or DBTS. Of the four cultures grown with DBT as sulphur source, the best growth occurred for the 32O-Yvgb plus 32O-W co-culture at 0·1 and 0·5 mmol l⁻¹ DBT. Although the presence of vgb provided no consistent advantage regarding growth on DBTS, strain 32O-W, as predicted by previous work, was shown to contain a partial 4S desulfurization pathway allowing it to metabolize this 4S pathway intermediate.     

Desulphurisation of benzothiophene and dibenzothiophene by actinomycete organisms belonging to the genus Rhodococcus, and related taxa

Desulphurising enzymes remove the sulphur moiety from an organosulphur molecule leaving the carbon skeleton intact. Two kinds of desulphurisation reaction are recognised. The dibenzothiophene (DBT)-specific pathway desulphurises DBT to inorganic sulphite and 2- hydroxybiphenyl (HBP), and the benzothiophene (BTH)-specific pathway desulphurises BTH to 2-(2-hydroxyphenyl)ethan 1-al (HPEal) and probably inorganic sulphite. The DBT-desulphurisation pathway was originally identified in Rhodococcus erythropolis strain IGTS8 (ATCC 53968), and the BTH-desulphurisation pathway in Gordonia sp. strain 213E (NCIMB 40816). These organisms do not further metabolise the organic product of desulphurisation.In this article current knowledge of the biochemistry and genetics of the desulphurisation enzymes is reviewed. The need for separate, DBT- and BTH-specific desulphurisation routes is rationalised in terms of the chemical differences between the two compounds. The desulphurisation pathway is compared with other microbial DBT- degrading enzyme systems. Finally some comments are made concerning the application of desulphurisation enzymes for fuel desulphurisation and on the relevance of these enzymes to the ecology of the mycolata (sensu Chun et al, 1996).     

The effect ofn-alkanes in the degradation of dibenzothiophene and of organic sulfur compounds in heavy oil by aPseudomonas sp.

Summary The microbial degradation of organic sulfur compounds was examined in aerobic conditions employing a pure culture of aPseudomonas sp., isolated from the soil. The effect ofn-alkanes on the degradation of dibenzothiophene (DBT) showed that the assimilation of the sulfur compound by the microorganism is favoured byn-dodecane. Moreover, the saturated fraction was seen to enhance the degradation of the sulfur compounds to be found in a deasphaltenated heavy oil.     

Desulfurization of Dibenzothiophene and Diesel Oils by a Newly Isolated Gordona Strain, CYKS1

A dibenzothiophene (DBT)-desulfurizing bacterial strain was isolated and identified as Gordona strain CYKS1. Strain CYKS1 was found to transform DBT to 2-hydroxybiphenyl via the 4S pathway and to be able to also use organic sulfur compounds other than DBT as a sole sulfur source. Its desulfurization activity was susceptible to sulfate repression. Active resting cells for desulfurization could be prepared only in the early growth phase. When two types of diesel oils, middle distillate unit feed (MDUF) and light gas oil (LGO) containing various organic sulfur compounds including DBT, were treated with resting cells of strain CYKS1 for 12 h, the total sulfur content significantly decreased, from 0.15% (wt/wt) to 0.06% (wt/wt) for MDUF and from 0.3% (wt/wt) to 0.25% (wt/wt) for LGO. The newly isolated strain CYKS1 is considered to have good potential for application in the biodesulfurization of fossil fuels.