Biodegradation Of Dibenzothiophene Research Articles

Hydro-Cracked Light Gas Oil Biodesulphurisation by Immobilised Pseudomonas aeruginosa Cells on Polyvinyl Alcohol

Abstract Refining petroleum fractions containing heterocyclic sulphur compounds to produce sulphur-free fuels, requires efficient desulphurisation methods. A new biocatalyst has been synthesised by immobilising Pseudomonas aeruginosa cells on polyvinyl alcohol by adsorption for hydro-cracked light gas oil bio-desulphurisation. The surface functional groups and biocatalyst morphology have been investigated by Fourier transform infrared spectroscopy and scanning electron microscopy. The bio-desulphurisation of dibenzothiophene as a heterocyclic sulphur model compound of gas oil was achieved with an aqueous-oil ratio (v/v) of 50 %, where the removed mass was 0.3826 mg per gram of biocatalyst at equilibrium condition, bio-desulphurisation rate of 0.375 h–1 and removal percentage was 95.65 %. The biodegradation of dibenzothiophene and its derivatives in hydro-cracked light gas oil has been determined after a batch process using 0.5 g of the biocatalyst after 5 h of contact time at 37 °C. According to gas chromatography - mass spectrometry, ethyl and trimethyl derivatives of dibenzothiophene have been degraded by higher efficiencies in comparison with other derivatives. Also, thiophenes and mercaptans of the gasoil sample have been degraded simultaneously to some extent. Equilibrium data have been observed to obey the pseudo-first-order kinetic model. The cell immobilisation facilitates the interaction of surface functional groups with sulphur compounds. The synergistic effect of cell immobilisation on the bio-activity of bacterial cells was due to the maintenance of the heterotrophic, bacillus morphology of the cells after immobilisation. This approach provides a simple, economical method with mild operating conditions to produce low-sulphur light gas oil through the biodegradation of heterocyclic sulphur compounds.

Effect of Rhodococcus bioaugmentation and biostimulation on dibenzothiophene biodegradation and bacterial community interaction in petroleum-contaminated soils

Bioremediation can be effective method for achieving polycyclic aromatic hydrocarbons (PAHs) degradation in soil contaminated with petroleum. The aim of this study was to compare the effect of Rhodococcus bioaugmentation (BIOE) and biostimulation (BIOS) on dibenzothiophene biodegradation and bacterial community interaction in petroleum-contaminated soils. The findings revealed that compared to natural degradation treatment (NAT) and BIOS, BIOE had the highest dibenzothiophene (DBT) and the majority of DBT degradation occurred within the first 30 days. BIOS had a positive impact in the early stage but an opposite effect in the later stages for degrading DBT. Beta diversity analysis revealed significant differences of bacterial composition among NAT, BIOS, and BIOE. Sequencing results indicated that Bacillus and Paenibacillus were dominant genera involved in DBT degradation. Network analysis revealed co-occurrence patterns and connectivity, with BIOE exhibiting higher connectivity and the highest number of links in BIOS. In summary, Rhodococcus bioaugmentation was the simplest and effective method to enhance the clustering degree of bacterial network and DBT degradation in petroleum-contaminated soil, compared to NAT and BIOS.

Insights into the Kinetics of the Microbial Degradation of Dibenzothiophene (DBT) by Acidithiobacillus ferrooxidans

Dibenzothiophene (DBT) is a major form of organo-sulfur compound chiefly found in coal. Acidithiobacillus ferrooxidans cells played the role of catalyst in degrading DBT to 2-hydroxy biphenyl (2HBP) through the formation of dibenzothiophene-sulfone and releasing the sulfur present in it. Experiments on the biodegradation of DBT by A. ferrooxidans bacterium using 9K medium with DBT at 3 g/L in a 500 mL shake flask scale achieved degradation of DBT up to 95% in 12 days. The A. ferrooxidans cells degrade DBT to 2-hydroxy biphenyl and release the sulfur atom in DBT through the formation of the intermediate dibenzothiophene-sulfone. The formation of 2HBP from microbial degradation of DBT followed the chemical control model of shrinking core reactions model in solid-liquid interactions. The kinetics of the DBT degradation by A. ferrooxidans followed first-order for a low initial concentration of DBT (3 g/L), and the kinetics were shifted to second-order with an increase in DBT concentration to 5 g/L.

Selective biodegradation of dibenzothiophene and alkyl dibenzothiophenes in crude oils from the Linpan oilfield, Bohai Bay basin, eastern China

The biodegradation of dibenzothiophene (DBT) and alkyl dibenzothiophenes (DBTs) were studied in crude oils from the Linpan oilfield, Bohai Bay basin, eastern China. The crude oils selected from the oilfield had been subjected to different degrees of biodegradation, i.e., non-biodegraded to severely biodegraded. With increasing biodegradation extent, the concentration of total DBTs in the crude oils rises from non- to heavily-biodegraded degrees, and then declines from heavily to severely-biodegraded degrees meanwhile the paraffins in the crude oils have been thoroughly removed. The differences in biodegradation rates had been observed between the homologues of alkyl DBTs, and the susceptibility to biodegradation of these homologues declines with increasing of the alkyl substituent number. Selective biodegradation occurred due to differences of carbon positions of alkyl substituents on molecular structure of DBTs. The sulfur-shielded isomers, such as 4,6-dimethyldibenzothiophene and 4-ethyl-6-methyldibenzothiophene, were more susceptible to biodegradation than the sulfur-exposed isomers, for example 2,8-dimethyldibenzothiophene and 1,2,7-+1,2,8-trimethyldibenzothiophenes (co-eluted as one peak in mass chromatograms). However, selective biodegradation of C4-DBTs isomers was less remarkable than the isomers of C2- and C3-DBTs, which reflected the complex processes of biodegradation.

Glycerol-assisted degradation of dibenzothiophene by Paraburkholderia sp. C3 is associated with polyhydroxyalkanoate granulation

Glycerol is a biodiesel byproduct. In the present study, glycerol was used as a co-substrate during biodegradation of dibenzothiophene (DBT) by Paraburkholderia sp. C3. Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent, ubiquitous and carcinogenic chemicals found in the environment. DBT is a major sulfur-containing PAH. The chemical properties of DBT make it an ideal model pollutant for examining the bioremediation of higher molecular weight PAHs. Bioremediation uses microbial catalysis for removal of environmental pollutants. Environmental microorganisms that encounter aromatic substrates such as heterocyclic PAHs develop unique characteristics that allow the uptake and assimilation of these cytotoxic substrates. Microbial adaptations include changes in membrane lipid composition, secretion of surface-active compounds and accumulation of lipid granules to withstand chemical toxicity. Biostimulation using more readily metabolized substrates can increase the biodegradation rate of PAHs, but the molecular mechanisms are not well understood. We analyzed the DBT biodegradation kinetics in C3, proteome changes and TEM micrographs in different culturing conditions. We utilized 2-bromoalkanoic lipid metabolic inhibitors to establish a correlation between polyhydroxyalkanoate (PHA) granule formation and the enhancement of DBT biodegradation induced by glycerol. This is the first description linking PHA biosynthesis, DBT biodegradation and 2-bromoalkanoic acids in a Paraburkholderia species.

Genome, metabolic pathways and characteristics of cometabolism of dibenzothiophene and the biodiesel byproduct glycerol in Paraburkholderia sp. C3

Utilization of glycerol, a biodiesel byproduct, has not been well explored. In the present study, glycerol and the other carbon sources were studied for cometabolism of dibenzothiophene (DBT), a model chemical commonly used in bioremediation studies, by Paraburkholderia sp. C3. This study showed a direct association between rhamnolipids (RLs) biosynthesis and DBT biodegradation induced by different carbon sources in a Paraburkholderia specie. Glycerol can induce the strain C3 produce at least four RLs. The RL precursor is mainly derived from the fatty acid synthesis (FAS II) and β-oxidation pathway. The genome contained two (fabF and fabG) and four (fadA, fadE, fadB and echA) genes involved in FAS II and β-oxidation, respectively. The genome also carried the rhlA and rhlB genes involved in rhamnosyltransferase for RL biosynthesis and two DBT dioxygenase genes (nahAc and catA). The findings suggest a viable approach of using the biodiesel byproduct glycerol to remediate contaminated environments.

Rhamnolipids Induced by Glycerol Enhance Dibenzothiophene Biodegradation in Burkholderia sp. C3

Abstract In highly urbanized areas, pollution from anthropogenic activities has compromised the integrity of the land, decreasing soil availability for agricultural practices. Dibenzothiophene (DBT) is a heterocyclic aromatic hydrocarbon frequently found in urbanized areas, and is often used as a model chemical to study the microbial transformation of pollutants. The potential for human exposure and its health risk makes DBT a chemical of concern; thus, it needs to be environmentally managed. We utilized glycerol to stimulate Burkholderia sp. C3 in order to degrade DBT in respect to ① DBT biodegradation kinetics, ② bacterial growth, ③ rhamnolipid (RL) biosynthesis, and ④ RL secretion. Under an optimum glycerol-to-DBT molar ratio, the DBT biodegradation rate constants increased up to 18-fold and enhanced DBT biodegradation by 25%–30% at day 1 relative to cultivation with DBT alone. This enhancement was correlated with an increase in bacterial growth and RL biosynthesis. Proteomics studies revealed the enzymes involved in the upper and main steps of RL biosynthesis. The RL congeners Rha-C10-C10, Rha-Rha-C10-C10, Rha-Rha-C10-C12, and Rha-Rha-C12-C12 were identified in the medium supplemented with glycerol and DBT, whereas only Rha-C12-C12 was identified in cultures without glycerol or with RL inhibitors. The studies indicated that glycerol enhances DBT biodegradation via increased RL synthesis and bacterial growth. The results warrant further studies of environmental biostimulation with glycerol to advance bioremediation technologies and increase soil availability for agricultural purposes.

Biodegradation of dibenzothiophene by efficient Pseudomonas sp. LKY-5 with the production of a biosurfactant

A potent bacterial strain capable of degrading dibenzothiophene (DBT) was isolated and evaluated for its characteristics. The strain, designated as LKY-5, is rod-shaped, gram-negative, and occurs mainly in clusters. It was identified as belonging to the Pseudomonas genus based on the 16S rDNA sequence and phylogenic analysis. Determination of its DBT depletion efficiency by gas chromatography revealed that the isolate was able to completely degrade up to 100 mg L−1 DBT within 144 h. The pH values, DBT concentrations, and biomasses in the medium varied significantly in the initial 24 h. A biosurfactant produced by LKY-5 was extracted and identified as a di-rhamnolipid with the formula Rha-Rha-C8-C8:1 by HPLC-ESI-MS/MS. There were 26 metabolites in the DBT degradation process. Pseudomonas sp. LKY-5 exhibited unusually high DBT degradation efficiency via multiple metabolic pathways. Compared with the reported 4S and Kodama pathways, two more expanded metabolic pathways for the degradation of DBT are proposed. The polycyclic aromatic sulfur heterocycles (PASHs) in diesel, such as C1-DBT, C2-DBT, C3-DBT, 4,6-DMDBT, and 2,4,6-TMDBT, can also be degraded with 28.2–42.3% efficiency. The results showed that LKY-5 is an excellent bacterial candidate for the bioremediation of PASH-contaminated sites and sediments.

Contribution of the Kodama and 4S pathways to the dibenzothiophene biodegradation in different coastal wetlands under different C/N ratios.

Dibenzothiophene (DBT) degradation mechanisms and the transformation of pathways during the incubation of three types of coastal sediments with C/N ratios ranging from 1 to 9 were investigated. The DBT degradation efficiencies were clearly improved with increasing C/N ratio in reed wetland sediments, tidal wetlands sediments and estuary wetland sediments. The quantitative response relationships between DBT degradation rates and related functional genes demonstrate that the Kodama pathway-related gene groups were dominant factors at low C/N ratios, while the 4S-related gene groups mainly determined the degradation rate when the C/N ratio was up to 5. Network analysis also shows that the pathway shifts from the Kodama pathway to the 4S pathway occurred through changes in the connections between functional genomes and rates. Furthermore, there were competition and collaboration between the Kodama and 4S pathways. The 4S pathway-related bacteria were more active in estuary wetland sediments compared with reed wetland sediments and tidal wetland sediments. The higher degradation efficiency in estuary wetland sediments may indicate the greater participation of the 4S pathway in the DBT biodegradation reaction. And the effects of ring cleavage of Kodama pathway caused more complete metabolizing of DBT.

Optimization of Substrate and Starter Cell Concentrations for Dibenzothiopene Biodegradation by Indigeneous Marine Bacteria <i>Mauricauda olearia</i> LBF-1-0009, <i>Alcanivorax xenomutants</i> LBF-1-0018, and <i>Stakelama pacifica</i> LBF-1-0031

Dibenzothiophene (DBT) and its derivatives have been widely used as model organic sulfur compounds in petroleum, included their biodegradation process. The abilities of microorganisms to degrade pollutants are significantly influenced by various factors such as microbial species, nutrients and environmental parameters. In this research, we carried out further study to determine optimal condition for DBT biodegradation regarding with substrate and strains cell concentration by several indigenous marine bacteria from Indonesia. These three isolates were belong to Mauricauda olearia, Alcanivorax xenomutants, and Stakelama pacifica, with homology result 99% each. Optimal dibenzothiophene as substrate reached by all isolates is 100 ppm, while cell concentration or microbial numbers that gave highest growth for all isolates is 20 based on conversion of OD600 nm measurement.

Optimization of Substrate and Starter Cell Concentrations for Dibenzothiopene Biodegradation by Indigeneous Marine Bacteria Mauricauda olearia LBF-1-0009, Alcanivorax xenomutants LBF-1-0018, and Stakelama pacifica LBF-1-0031

Dibenzothiophene (DBT) and its derivatives have been widely used as model organic sulfur compounds in petroleum, included their biodegradation process. The abilities of microorganisms to degrade pollutants are significantly influenced by various factors such as microbial species, nutrients and environmental parameters. In this research, we carried out further study to determine optimal condition for DBT biodegradation regarding with substrate and strains cell concentration by several indigenous marine bacteria from Indonesia. These three isolates were belong to Mauricauda olearia, Alcanivorax xenomutants, and Stakelama pacifica, with homology result 99% each. Optimal dibenzothiophene as substrate reached by all isolates is 100 ppm, while cell concentration or microbial numbers that gave highest growth for all isolates is 20 based on conversion of OD600 nm measurement.

Main and Interactive Effects of Polyaromatic Sulfur Heterocyclic Compounds on Growth and Biodegradation Efficiencies of Bacillus sphaericus HN1: Modeling and Statistical Analysis

Bioremediation is an effective technique to remediate soil and water contaminated with a mixture of recalcitrant polyaromatic sulfur heterocyclic (PASH) compounds. Based on two levels of full factorial design, a statistical design of experiments was used in this study to investigate the interactive effects of three PASHs; thiophene (Th), benzothiophene (BT), and dibenzothiophene (DBT) on their biodegradation in multisubstrate batch process using Bacillus sphaericus HN1. Kinetic modeling was performed to estimate the rate of biodegradation of each PASH in single-, binary-, and tertiary-substrate systems. Biodegradation of BT, DBT, and total PASHs follows the first order kinetic reaction in the single- and multisubstrate batch systems, while biodegradation of Th follows the first-order kinetic reaction, in single-substrate system, but second-order kinetic reaction in multisubstrate batch system. Four linear interaction regression models were estimated and validated to describe the interactive effect of the three PASHs on their biodegradation. Statistical analysis of the results in the form of analysis of variance and Student t test indicated significant role played by the main effects of Th, BT and DBT on their biodegradation (p < 0.01). Th and the interactive effect between Th and DBT has statistically significant negative effect on DBT removal (p = 0.0665). However, DBT expresses higher statistically significant positive effect on total PASHs removal than that of Th (p = 0.0178 and p = 0.026, respectively), but their interaction has a significantly negative effect (p = 0.0143).

Modeling and Simulation for Biodegradation of Mono-, Binary-, and Tertiary-substrate Batch Systems of Different Polyaromatic Sulfur Heterocyclic Compounds

Biodegradation kinetics of different polyaromatic sulfur heterocyclic compounds (PASHs): thiophene (Th), benzothiophene (BT), and dibenzothiophene (DBT) in a series of batch experiments were investigated as mono-, binary-, and tertiary-substrate systems to study the substrates interaction effect and capabilities of Bacillus sphaericus HN1 to utilize PASHs as sole carbon and energy source in mono- and multi-substrate systems. A multiple comparison test was performed for growth of microorganism and substrate biodegradation to obtain pairwise comparison between the three studied systems. Both tests ANOVA1 and Kruskal-Wallis showed that there was a highly statistically significant difference in growth of HN1 between negative control (free of PASHs) and all other treatments (p = 2.2105e-7 and 9.303e-4, respectively). Although, there was a statistically significant difference for biodegradation of DBT in mono– and binary-substrate systems within the time interval 96–168 h (p < 0.05), but there was a nonstatistically significant difference in the biodegradation of both Th and BT in the three studied systems (p > 0.05). A multi-substrate form of the Monod kinetic model was applied to predict the substrate interactions in binary- and tertiary-substrate systems using the Monod parameters derived from the mono-substrate systems. Simulation of the applied models to describe and estimate the biodegradation kinetics of the three studied PASHs in the different investigated systems was performed and the validity of the models was confirmed.

Biological Removal of Dibenzothiophene from Soil and Changes to soil Sulfate by White-Rot Fungus Phanerochaete chrysosporium

This study investigated biodegradation of dibenzothiophene (DBT) in marsh soil spiked bywhite-rot fungus Phanerochaete chrysosporium. Soil samples were spiked with 100 ppm DBTand incubated at 30°C in a dark chamber for 30 days. Samples were evaluated for pH, Mnperoxidaseactivity, sulfate ion concentration and growth during the tests. Results showedmaximum levels of pH, Mn-peroxidase and sulfate concentrations at 8.19, 66 U L-1 and 31.21mg kg-1 respectively. Colony forming unit assay determinations for contaminated soil samplesshowed that the fungus was able to grow and use dibenzothiophene as a source of carbon andenergy. GC analysis of contaminated samples compared to control samples, demonstrateddegradation of DBT by Phanerochaete chrysosporium. There was no significantly improvedeffect on degradation when the treatment was performed in presence of soil micro flora. Thesystem attained a high rate of DBT degradation at approximately 83.34%, the 30 day testoperation under optimal conditions. After 20 days, the sulfate ion concentration in soil sampleshad almost doubled.

The Study of Degradation Characteristics of Isolated &lt;i&gt;Pseudomonas&lt;/i&gt; Sp. LKY-5 on Dibenzothiophene

Dibenzothiophene (DBT) may seriously pollute the environment with its mutagenicity, teratogenicity and carcinogenicity. And it is recalcitrant to be degraded by microorganisms due to its low bioavailability and high hydrophobicity. In this paper, the five parameters, namely, initial concentration, temperature, pH, agitation rate and inoculum size were experimented and studied by the isolated Pseudomonas sp. LKY-5 for degradation processes. The results shown that the initial concentration of 100 mg/L, temperature of 30°C, pH of 7.5, agitation rate of 160 rpm, inoculum size of 10 % were optimal for the biodegradation of dibenzothiophene.

Enhancing Biodegradation of Dibenzothiophene by Bacillus sphaericus HN1 Using Factorial Design and Response Surface Optimization of Medium Components

Based on four levels of full factorial design, a statistical design of experiments is used to investigate two cases of dibenzothiophene biodegradation in batch processes using Bacillus sphaericus HN1, involving as factors, yeast extract and dimethylsulfoxide or magnesium sulfate for first and second cases, respectively. Predictive models have been correlated finding out how significant the effects of these variables (factors) and their interactions are in practice. Also, response surface methodology has been applied to visualize the effect of the studied factors and LINGO software was used to find out the optimum values of the variables for enhancing the process.

C–S Targeted Biodegradation of Dibenzothiophene by Stenotrophomonas sp. NISOC-04

Crude oil-contaminated soil samples were gathered across Khuzestan oilfields (National Iranian South Oil Company, NISOC) consequently experienced a screening procedure for isolating C-S targeted dibenzothiophene-biodegrading microorganisms with previously optimized techniques. Among the isolates, a bacterial strain was selected due to its capability of biodegrading dibenzothiophene in a C-S targeted manner in aqueous phases and medium mostly consisting of separately biphasic water-gasoline. The 16S rDNA of the isolate was amplified using eubacterial-specific primers and then sequenced. Based on sequence data analysis, the microorganism, designated NISOC-04, clustered most closely with the members of the genus Stenotrophomonas. Gas chromatography indicated that Stenotrophomonas sp. NISOC-04 utilizes 82% of starting 0.8 mM dibenzothiophene within a 48-h-long exponential growth phase. Growth curve analysis revealed the inability of Stenotrophomonas sp. NISOC-04 to utilize dibenzothiophene (DBT) as the exclusive carbon or carbon/sulfur source. Gibbs' assay showed no 2-hydroxy biphenyl accumulation, but HPLC confirmed the presence of 2-hydroxy biphenyl as the final product of DBT desulfurization. Under sulfur starvation, Stenotrophomonas sp. NISOC-04 produced a huge biomass with untraceable sulfur and utilized atmospheric insignificant sulfur levels.

Ultraviolet treatment and biodegradation of dibenzothiophene: Identification and toxicity of products.

Biodegradation of pollutants often results in incomplete mineralization and formation of degradation products with unknown chemical and toxicological characteristics. Ultraviolet (UV) irradiation, a common technology used in water and wastewater treatment, may help reduce aqueous concentrations of degradation products produced during biological treatment and their associated hazards. Combined biological and UV transformations may be important in natural systems as well. We investigated the effects of UV irradiation (254 nm) on dibenzothiophene (DBT), a sulfur-containing polyaromatic hydrocarbon, in artificial seawater, and its effects on biodegradation products produced from mixed-community microbial transformations of DBT, including DBT sulfone, DBT sulfoxide, hydroxylated and carboxylated benzothiophenes, thiosalicylic acid, and others. Toxicity of solutions after UV exposure was monitored using bioluminescent bacteria (Vibrio fischeri) and by evaluating cardiac deformities in Fundulus heteroclitus embryos. The highest UV fluence reduced DBT concentration by 28% when DBT was present as the sole organic solute. In postbiodegradation solution, the same fluence reduced the initial concentration of DBT by 81%, and 11 DBT biodegradation products to trace levels. Regardless of UV fluence, DBT by itself produced minimal effects in Fundulus embryos but was moderately toxic to V. fischeri. Postbiodegradation solutions were highly toxic to both test organisms. The highest UV fluence slightly reduced toxicity of postbiodegradation solution to V. fischeri but exacerbated cardiac deformities in Fundulus embryos. Toxicity could not be attributed to specific products and was likely a result of mixture effects. These results emphasize that toxicity can increase during remediation and that multiple assays may be necessary for evaluation. The novel approach of combined biodegradation/UV treatment is promising, although further research is needed to reduce toxicity in the case of DBT.

Biodegradation of dibenzothiophene, fluoranthene, pyrene and chrysene in a soil slurry reactor by the white-rot fungus Bjerkandera sp. BOS55

Mass transfer phenomena can be an important constraint of the soil remediation process. With the goal of minimizing the mass transfer limitation, the degradation of four different PAHs by the white-rot fungus Bjerkandera adusta in a spiked marsh soil was evaluated in a slurry system. Key factors affecting the oxidation of PAHs with different chemical structure (two, three and four aromatic rings) were investigated. These included inoculum preparation, glucose concentration and synergic or antagonic actions between endogenous microflora and fungal culture. It was demonstrated that the fungus was able to grow and degrade the pollutants in a slurry phase stirred tank reactor. There was no significant improved effect on the degradation when the treatment was performed in presence of soil microflora. The system attained high PAH degradations, around 30 mg PAH/kg soil, after 30 days of operation under optimal conditions.

Aerobic Biodegradation of 2,2′-Dithiodibenzoic Acid Produced from Dibenzothiophene Metabolites

Dibenzothiophene is a sulfur heterocycle found in crude oils and coal. The biodegradation of dibenzothiophene through the Kodama pathway by Pseudomonas sp. strain BT1d leads to the formation of three disulfides: 2-oxo-2-(2-thiophenyl)ethanoic acid disulfide, 2-oxo-2-(2-thiophenyl)ethanoic acid-2-benzoic acid disulfide, and 2,2'-dithiodibenzoic acid. When provided as the carbon and sulfur source in liquid medium, 2,2'-dithiodibenzoic acid was degraded by soil enrichment cultures. Two bacterial isolates, designated strains RM1 and RM6, degraded 2,2'-dithiodibenzoic acid when combined in the medium. Isolate RM6 was found to have an absolute requirement for vitamin B12, and it degraded 2,2'-dithiodibenzoic acid in pure culture when the medium was supplemented with this vitamin. Isolate RM6 also degraded 2,2'-dithiodibenzoic acid in medium containing sterilized supernatants from cultures of isolate RM1 grown on glucose or benzoate. Isolate RM6 was identified as a member of the genus Variovorax using the Biolog system and 16S rRNA gene analysis. Although the mechanism of disulfide metabolism could not be determined, benzoic acid was detected as a transient metabolite of 2,2'-dithiodibenzoic acid biodegradation by Variovorax sp. strain RM6. In pure culture, this isolate mineralized 2,2'-dithiodibenzoic acid, releasing 59% of the carbon as carbon dioxide and 88% of the sulfur as sulfate.