Substrate interactions during the biodegradation of BTEX and THF mixtures by Pseudomonas oleovorans DT4

The efficient tetrahydrofuran (THF)-degrading bacterium, Pseudomonas oleovorans DT4 was used to investigate the substrate interactions during the aerobic biotransformation of THF and BTEX mixtures. Benzene and toluene could be utilized as growth substrates by DT4, whereas cometabolism of m-xylene, p-xylene and ethylbenzene occurred with THF. In binary mixtures, THF degradation was delayed by xylene, ethylbenzene, toluene and benzene in descending order of inhibitory effects. Conversely, benzene (or toluene) degradation was greatly enhanced by THF leading to a higher degradation rate of 39.68 mg/(h g dry weight) and a shorter complete degradation time about 21 h, possibly because THF acted as an “energy generator”. Additionally, the induction experiments suggested that BTEX and THF degradation was initiated by independent and inducible enzymes. The transient intermediate hydroquinone was detected in benzene biodegradation with THF while catechol in the process without THF, suggesting that P. oleovorans DT4 possessed two distinguished benzene pathways.     

Isolation and characterization of ethylbenzene degrading <Emphasis Type="Italic">Pseudomonas putida</Emphasis> E41

Pseudomonas putida E41 was isolated from oil-contaminated soil and showed its ability to grow on ethyl-benzene as the sole carbon and energy source. Moreover, P. putida E41 show the activity of biodegradation of ethylbenzene in the batch culture. E41 showed high efficiency of biodegradation of ethylbenzene with the optimum conditions (a cell concentration of 0.1 g wet cell weight/L, pH 7.0, 25°C, and ethylbenzene concentration of 50 mg/L) from the results of the batch culture. The maximum degradation rate and specific growth rate (μ_max) under the optimum conditions were 0.19+0.03 mg/mg-DCW (Dry Cell Weight)/h and 0.87+0.13 h⁻¹, respectively. Benzene, toluene and ethylbenzene were degraded when these compounds were provided together; however, xylene isomers persisted during degradation by P. putida E41. When using a bioreactor batch system with a binary culture with P. putida BJ10, which was isolated previously in our lab, the degradation rate for benzene and toluene was improved in BTE mixed medium (each initial concentration: 50 mg/L). Almost all of the BTE was degraded within 4 h and 70–80% of m-, p-, and o-xylenes within 11 h in a BTEX mixture (initial concentration: 50 mg/L each). In summary, we found a valuable new strain of P. putida, determined the optimal degradation conditions for this isolate and tested a mixed culture of E41 and BJ10 for its ability to degrade a common sample of mixed contaminants containing benzene, toluene, and xylene.     

Biotreatment of groundwater contaminated with MTBE: interaction of common environmental co-contaminants

Contamination of groundwater with the gasoline additive methyl tert-butyl ether (MTBE) is often accompanied by many aromatic components such as benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene (BTEX). In this study, a laboratory-scale biotrickling filter for groundwater treatment inoculated with a microbial consortium degrading MTBE was studied. Individual or mixtures of BTEX compounds were transiently loaded in combination with MTBE. The results indicated that single BTEX compound or BTEX mixtures inhibited MTBE degradation to varying degrees, but none of them completely repressed the metabolic degradation in the biotrickling filter. Tert-butyl alcohol (TBA), a frequent co-contaminant of MTBE had no inhibitory effect on MTBE degradation. The bacterial consortium was stable and showed promising capabilities to remove TBA, ethylbenzene and toluene, and partially degraded benzene and xylenes without significant lag time. The study suggests that it is feasible to deploy a mixed bacterial consortia to degrade MTBE, BTEX and TBA at the same time.     

Bioremediation Assessment of a BTEX‐Contaminated Soil

The elimination of BTEX (benzene, toluene, ethylbenzene, o‐xylene) compounds from soil was studied. After 18 days at 20 °C, 21% of the initial total BTEX contamination (400 mg/kg soil) was lost due to sorption onto soil. Biodegradation decreased in the order ethylbenzene > toluene > benzene > o‐xylene. NPK fertilisation stimulated biodegradation, particularly that of benzene and toluene, significantly, and oleophilic fertilisation inhibited biodegradation. After 18 days, the residual contamination in the NPK‐fertilised, unfertilised and with oleophilic nutrients amended soil was 96, 166 and 196 mg total BTEX/kg soil, respectively. The presence of BTEX initially inhibited the biological activity of the soil (fluorescein diacetate hydrolysis) considerably. This short‐term, reversible inhibition was significantly higher in the unfertilised soil than in the fertilised soil.     

Kinetics of BTEX biodegradation by a coculture of <Emphasis Type="Italic">Pseudomonas putida</Emphasis> and<Emphasis Type="Italic"> Pseudomonas fluorescens</Emphasis> under hypoxic conditions

Pseudomonas putida and Pseudomonas fluorescens present as a coculture were studied for their abilities to degrade benzene, toluene, ethylbenzene, and xylenes (collectively known as BTEX) under various growth conditions. The coculture effectively degraded various concentrations of BTEX as sole carbon sources. However, all BTEX compounds showed substrate inhibition to the bacteria, in terms of specific growth, degradation rate, and cell net yield. Cell growth was completely inhibited at 500mgl^–1 of benzene, 600mgl^–1 of o-xylene, and 1000mgl^–1 of toluene. Without aeration, aerobic biodegradation of BTEX required additional oxygen provided as hydrogen peroxide in the medium. Under hypoxic conditions, however, nitrate could be used as an alternative electron acceptor for BTEX biodegradation when oxygen was limited and denitrification took place in the culture. The carbon mass balance study confirmed that benzene and toluene were completely mineralized to CO₂ and H₂O without producing any identifiable intermediate metabolites.     

Anaerobic Degradation of Benzene, Toluene, Ethylbenzene, and o-Xylene in Sediment-Free Iron-Reducing Enrichment Cultures

Monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene (BTEX) are widespread contaminants in groundwater. We examined the anaerobic degradation of BTEX compounds with amorphous ferric oxide as electron acceptor. Successful enrichment cultures were obtained for all BTEX substrates both in the presence and absence of AQDS (9,10-anthraquinone-2,6-disulfonic acid). The electron balances showed a complete anaerobic oxidation of the aromatic compounds to CO₂. This is the first report on the anaerobic degradation of o-xylene and ethylbenzene in sediment-free iron-reducing enrichment cultures.     

Lab-Scale Biodegradation Study of BTEX under the Unsaturated Condition and Its Effect on Soil Matric Potential

Benzene, toluene, ethylbenzene, and xylene are collectively known as BTEX which contributes to volatile environmental contaminants. This present study investigates the microbial degradation of BTEX in batch and continuous soil column experiments and its effects on soil matric potential. Batch degradation experiments were performed with different initial concentrations of BTEX using the BTEX tolerant culture isolated from petroleum-contaminated soil. In batch study, the degradation pattern for single substrate showed that xylene was degraded much faster than other compounds followed by ethylbenzene, toluene, and benzene with the highest μ_max = 0.140 h^?1 during initial substrate concentration of 100 mg L^?1. Continuous degradation experiments were performed in a soil column with an inlet concentration of BTEX of about 2000 mg L^?1 under unsaturated flow in anaerobic condition. BTEX degradation pattern was studied with time and the matric potential of the soil at different parts along the length of the column were determined at the end of the experiment. In continuous degradation study, BTEX compounds were degraded with different degradation pattern and an increase in soil matric potential was observed with an increase in depth from top to bottom in the column with applied suction head. It was found that column biodegradation contributed to 69.5% of BTEX reduction and the bacterial growth increased the soil matric potential of about 34% on an average along the column height. Therefore, this study proves that it is significant to consider soil matric potential in modeling fate and transport of BTEX in unsaturated soils.     

Temperature effects and substrate interactions during the aerobic biotransformation of BTEX mixtures by toluene-enriched consortia and Rhodococcus rhodochrous

A microbial consortium derived from a gasoline-contaminated aquifer was enriched on toluene (T) in a chemostat at 20 degrees C and was found to degrade benzene (B), ethylbenzene (E), and xylenes (X). Studies conducted to determine the optimal temperature for microbial activity revealed that cell growth and toluene degradation were maximized at 35 degrees C. A consortium enriched at 35 degrees C exhibited increased degradation rates of benzene, toluene, ethylbenzene, and xylenes in single-substrate experiments; in BTEX mixtures, enhanced benzene, toluene, and xylene degradation rates were observed, but ethylbenzene degradation rates decreased. Substrate degradation patterns over a range of BTEX concentrations (0 to 80 mg/L) for individual aromatics were found to differ significantly from patterns for aromatics in mixtures. Individually, toluene was degraded fastest, followed by benzene, ethylbenzene, and the xylenes. In BTEX mixtures, degradation followed the order of ethylbenzene, toluene, and benzene, with the xylenes degraded last. A pure culture isolated from the 35 degrees C-enriched consortium was identified as Rhodococcus rhodochrous. This culture was shown to degrade each of the BTEX compounds, individually and in mixtures, following the same degradation patterns as the mixed cultures. Additionally, R. rhodochrous was shown to utilize benzene, toluene, and ethylbenzene as primary carbon and energy sources. Studies conducted with the 35 degrees C-enriched consortium and R. rhodochrous to evaluate potential substrate interactions caused by the concurrent presence of multiple BTEX compounds revealed a range of substrate interaction patterns including no interaction, stimulation, competitive inhibition, noncompetitive inhibition, and cometabolism. In the case of the consortium, benzene and toluene degradation rates were slightly enhanced by the presence of o-xylene, whereas the presence of toluene, benzene, or ethylbenzene had a negative effect on xylene degradation rates. Ethylbenzene was shown to be the most potent inhibitor of BTEX degradation by both the mixed and pure cultures. Attempted quantification of these inhibition effects in the case of the consortium suggested a mixture of competitive and noncompetitive inhibition kinetics. Benzene, toluene, and the xylenes had a negligible effect on the biodegradation of ethylbenzene by both cultures. Cometabolism of o-, m-, and p-xylene was shown to be a positive substrate interaction.     

Substrate Interactions during the Biodegradation of Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) Hydrocarbons by the Fungus Cladophialophora sp. Strain T1

The soil fungus Cladophialophora sp. strain T1 (= ATCC MYA-2335) was capable of growth on a model water-soluble fraction of gasoline that contained all six BTEX components (benzene, toluene, ethylbenzene, and the xylene isomers). Benzene was not metabolized, but the alkylated benzenes (toluene, ethylbenzene, and xylenes) were degraded by a combination of assimilation and cometabolism. Toluene and ethylbenzene were used as sources of carbon and energy, whereas the xylenes were cometabolized to different extents. o-Xylene and m-xylene were converted to phthalates as end metabolites; p-xylene was not degraded in complex BTEX mixtures but, in combination with toluene, appeared to be mineralized. The metabolic profiles and the inhibitory nature of the substrate interactions indicated that toluene, ethylbenzene, and xylene were degraded at the side chain by the same monooxygenase enzyme. Our findings suggest that soil fungi could contribute significantly to bioremediation of BTEX pollution.     

Degradation of BTEX compounds in liquid media and in peat biofilters

A mixed culture, enriched from Sphagnum peat moss, contaminated with gasoline vapours, degraded individual and mixed components of BTEX (benzene, toluene, ethylbenzene, xylene). Complete degradation of radiolabelled toluene by the mixed culture was observed in mineralisation studies. Individual isolates from a mixed culture containingPseudomonas maltophilia, P. testosteroni andP. putida biotype A exhibited contrasting BTEX degradation patterns. WhileP. putida biotype A degraded all of the BTEX compounds,P. maltophilia andP. testosteroni, appeared unable to degrade benzene and xylenes, respectively. When the peat, inoculated with the mixed culture, was used as a biofilter (6.2 cm diameter ×93 cm length) for degradation of toluene and ethylbenzene vapours, percentage removal efficiencies were 99 and 85, respectively. When the capacity of the biofilter to degrade a combination of BTEX compounds was evaluated, percentage removal efficiencies for toluene, ethylbenzene,p-xylene,o-xylene and benzene were 99, 85, 82, 80 and 78, respectively. The importance of using the mixed culture as an inoculum in the biofilter was established and also the relationship between contaminated vapour flow rate and percentage removal efficiency.     

Anaerobic degradation of benzene, toluene, ethylbenzene, and o-xylene in sediment-free iron-reducing enrichment cultures

Monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene (BTEX) are widespread contaminants in groundwater. We examined the anaerobic degradation of BTEX compounds with amorphous ferric oxide as electron acceptor. Successful enrichment cultures were obtained for all BTEX substrates both in the presence and absence of AQDS (9,10-anthraquinone-2,6-disulfonic acid). The electron balances showed a complete anaerobic oxidation of the aromatic compounds to CO2. This is the first report on the anaerobic degradation of o-xylene and ethylbenzene in sediment-free iron-reducing enrichment cultures.     

Mesophilic and thermophilic BTEX substrate interactions for a toluene-acclimatized biofilter

Benzene, toluene, ethylbenzene and xylene (BTEX) substrate interactions for a mesophilic (25°C) and thermophilic (50°C) toluene-acclimatized composted pine bark biofilter were investigated. Toluene, benzene, ethylbenzene, o-xylene, m-xylene and p-xylene removal efficiencies, both individually and in paired mixtures with toluene (1:1 ratio), were determined at a total loading rate of 18.1 g m^–3 h^–1 and retention time ranges of 0.5–3.0 min and 0.6–3.8 min for mesophilic and thermophilic biofilters, respectively. Overall, toluene degradation rates under mesophilic conditions were superior to degradation rates of individual BEX compounds. With the exception of p-xylene, higher removal efficiencies were achieved for individual BEX compounds compared to toluene under thermophilic conditions. Overall BEX compound degradation under mesophilic conditions was ranked as ethylbenzene >benzene >o-xylene >m-xylene >p-xylene. Under thermophilic conditions overall BEX compound degradation was ranked as benzene >o-xylene >ethylbenzene >m-xylene >p-xylene. With the exception of o-xylene, the presence of toluene in paired mixtures with BEX compounds resulted in enhanced removal efficiencies of BEX compounds, under both mesophilic and thermophilic conditions. A substrate interaction index was calculated to compare removal efficiencies at a retention time of 0.8 min (50 s). A reduction in toluene removal efficiencies (negative interaction) in the presence of individual BEX compounds was observed under mesophilic conditions, while enhanced toluene removal efficiency was achieved in the presence of other BEX compounds, with the exception of p-xylene under thermophilic conditions.     

Application of aerobic microorganisms in bioremediation in situ of soil contaminated by petroleum products

Aerobic microorganisms able to biodegrade benzene, toluene, ethylbenzene, xylene (BTEX) have been isolated from an area contaminated by petroleum products. The activity of the isolated communities was tested under both laboratory and field conditions. Benzene, toluene, ethylbenzene and xylene were added to the cultures as the sole carbon source, at a concentration of 500 mg/L. In batch cultures under laboratory conditions, an 84% reduction of benzene, 86% of toluene and 82% of xylene were achieved. In cultures with ethylbenzene as the sole carbon source, the reduction was around 80%. Slightly lower values were observed under field conditions: 95% reduction of benzene and toluene, 81% of ethylbenzene and 80% of xylene. A high biodegradation activity of benzene (914 μM/L/24 h), toluene (771 μM/L/24 h), xylene (673 μM/L/24 h) and ethylbenzene (644 μM/L/24 h) was observed in the isolated communities.     

Microbial communities and biodegradation in lab-scale BTEX-contaminated groundwater remediation using an oxygen-releasing reactive barrier

To remediate benzene, toluene, ethylbenzene and xylene (BTEX) -contaminated groundwater, a biotreatment process including biostimulation and bioaugmentation was simulated using oxygen-releasing reactive barriers (ORRB) and water with added BTEX in a lab-scale system. The results showed that the capability for BTEX removal decreases in the order of benzene, toluene, p-xylene, ethylbenzene for both added-nitrogen and no-added-nitrogen under BTEX concentrations at 30 mg l⁻¹. The removal efficiencies in ORRB systems were higher in the nitrogen-added condition for biostimulation compared with the no-nitrogen-added condition; moreover, an increased pattern for removal was observed during the bioaugmentation process. The oxygen content was found to be inversely proportional to the distance from the ORRB, as evidenced by observing that the average bacteria densities were two orders higher when located at 15 cm compared with 30 cm from the ORRB. The microbial community structure was similar in both cases of added-nitrogen and the no-added-nitrogen conditions.     

Comparative Genomic Analysis and Benzene,Toluene, Ethylbenzene,and o-, m-, and p-Xylene (BTEX) Degradation Pathways of Pseudoxanthomonas spadix BD-a59

Pseudoxanthomonas spadix BD-a59, isolated from gasoline-contaminated soil, has the ability to degrade all six BTEX (benzene, toluene, ethylbenzene, and o-, m-, and p-xylene) compounds. The genomic features of strain BD-a59 were analyzed bioinformatically and compared with those of another fully sequenced Pseudoxanthomonas strain, P. suwonensis 11-1, which was isolated from cotton waste compost. The genome of strain BD-a59 differed from that of strain 11-1 in many characteristics, including the number of rRNA operons, dioxygenases, monooxygenases, genomic islands (GIs), and heavy metal resistance genes. A high abundance of phage integrases and GIs and the patterns in several other genetic measures (e.g., GC content, GC skew, Karlin signature, and clustered regularly interspaced short palindromic repeat [CRISPR] gene homology) indicated that strain BD-a59''s genomic architecture may have been altered through horizontal gene transfers (HGT), phage attack, and genetic reshuffling during its evolutionary history. The genes for benzene/toluene, ethylbenzene, and xylene degradations were encoded on GI-9, -13, and -21, respectively, which suggests that they may have been acquired by HGT. We used bioinformatics to predict the biodegradation pathways of the six BTEX compounds, and these pathways were proved experimentally through the analysis of the intermediates of each BTEX compound using a gas chromatograph and mass spectrometry (GC-MS). The elevated abundances of dioxygenases, monooxygenases, and rRNA operons in strain BD-a59 (relative to strain 11-1), as well as other genomic characteristics, likely confer traits that enhance ecological fitness by enabling strain BD-a59 to degrade hydrocarbons in the soil environment.     

BTEX-Contaminated Gas Treatment in a Shallow, Sparged, Suspended-Growth Bioreactor

Treatment of a gas contaminated with a mixture of benzene, toluene, ethylbenzene, and o-xylene (BTEX) compounds in a 40-cm-deep laboratory-scale bioreactor containing suspended biomass was investigated. Gas treatment efficiency was not significantly impacted by different BTEX mixtures, and approximately 99% removal was achieved for volumetric loadings of 11 to 18 mg-BTEX/L-reactor volume/hr (specific biomass loadings of 0.27 to 0.83 g-BTEX/g-VSS/d; inlet concentrations of total BTEX of 2.3 to 4.3 mg/L) and operational solids retention times (SRTs) of 1.7, 2.7, and 9.2 days. Maximum specific biodegradation rates of the reactor biomass increased as the reactor SRTs decreased. Under specific loadings greater than 1 g-BTEX/g-VSS/d the gas treatment became biokinetically limited, such that BTEX and unidentified BTEX metabolites accumulated in the bioreactor liquid over time. BTEX gas-liquid mass transfer was sufficient in the 40-cm-deep sparged liquid reactor to provide high BTEX treatment efficiency.     

Methyl tert-butyl ether (MTBE) degradation by a microbial consortium

The widespread use of methyl tert-butyl ether (MTBE) as a gasoline additive has resulted in a large number of cases of groundwater contamination. Bioremediation is often proposed as the most promising alternative after treatment. However, MTBE biodegradation appears to be quite different from the biodegradation of usual gasoline contaminants such as benzene, toluene, ethyl benzene and xylene (BTEX). In the present paper, the characteristics of a consortium degrading MTBE in liquid cultures are presented and discussed. MTBE degradation rate was fast and followed zero order kinetics when added at 100 mg l(-1). The residual MTBE concentration in batch degradation experiments ranged from below the detection limit (1 microg l(-1)) to 50 microg l(-1). The specific activity of the consortium ranged from 7 to 52 mgMTBE g(dw)(-1) h(-1) (i.e. 19-141 mgCOD g(dw) (-1) h(-1)). Radioisotope experiments showed that 79% of the carbon-MTBE was converted to carbon-carbon dioxide. The consortium was also capable of degrading a variety of hydrocarbons, including tert-butyl alcohol (TBA), tert-amyl methyl ether (TAME) and gasoline constituents such as benzene, toluene, ethylbenzene and xylene (BTEX). The consortium was also characterized by a very slow growth rate (0.1 d(-1)), a low overall biomass yield (0.11 gdw g(-1)MTBE; i.e. 0.040 gdw gCOD(-1)), a high affinity for MTBE and a low affinity for oxygen, which may be a reason for the slow or absence of MTBE biodegradation in situ. Still, the results presented here show promising perspectives for engineering the in situ bioremediation of MTBE.     

Thermophilic biodegradation of BTEX by two Thermus Species

Two thermophilic bacteria, Thermus aquaticus ATCC 25104 and Thermus species ATCC 27978, were investigated for their abilities to degrade BTEX (benzene, toluene, ethylbenzene, and xylenes). Thermus aquaticus and the Thermus sp. were grown in a nominal medium at 70 degrees C and 60 degrees C, respectively, and resting cell suspensions were used to study BTEX biodegradation at the same corresponding temperatures. The degradation of BTEX by these cell suspensions was measured in sealed serum bottles against controls that also displayed significant abiotic removals of BTEX under such high-temperature conditions. For T. aquaticus at a suspension density of only 1.3 x 10(7) cells/mL and an aqueous total BTEX concentration of 2.04 mg/L (0.022 mM), benzene, toluene, ethylbenzene, m-xylene, and an unresolved mixture of o-and p-xylenes were biodegraded by 10, 12, 18, 20, and 20%, respectively, after 45 days of incubation at 70 degrees C. For the Thermus sp. at a suspension density of 1.1 x 10(7) cells/mL and an aqueous total BTEX concentration of 6.98 mg/L (0.079 mM), benzene, toluene, ethylbenzene, m-xylene, and the unresolved mixture of o-and p-xylenes were biodegraded by 40, 35, 32, 33, and 33%, respectively, after 45 days of incubation at 60 degrees C. Raising the BTEX concentrations lowered the extents of biodegradation. The biodegradations of both benzene and toluene were enhanced when T. aquaticus and the Thermus sp. were pregrown on catechol and o-cresol, respectively, as carbon sources. Use of [U-(14)C]benzene and [ring-(14)C]toluene verified that a small fraction of these two compounds was metabolized within 7 days to water-soluble products and CO(2) by these nongrowing cell suspensions. Our investigation also revealed that the nominal medium can be simplified by eliminating the yeast extract and using a higher tryptone concentration (0.2%) without affecting the growth and BTEX degrading activities of these cells. (c) 1995 John Wiley & Sons, Inc.     

Utilization of monocyclic aromatic hydrocarbons individually and in mixture by bacteria isolated from petroleum-contaminated soil

The fate of benzene, ethylbenzene, toluene, xylenes (BTEX) compounds through biodegradation was investigated using two different bacteria, Ralstonia picketti (BP-20) and Alcaligenes piechaudii (CZOR L-1B). These bacteria were isolated from extremely polluted soils contaminated with petroleum hydrocarbons. PCR and Fatty Acid Methyl Ester (FAME) were used to identify the isolates. In this study, BTEX biodegradation, applied as a mixture or as individual compounds by the bacteria was evaluated. Both bacteria were shown to degrade each of the BTEX compounds individually and in mixture. However, Alcaligenes piechaudii was a better degrader of BTEXs both in the mixture and individually. Differences between BTEX biodegradation in the mixture and individually were observed, especially in the case of benzene. The degradation of all BTEXs in the mixture was lower than the degradation of individual compounds for both bacteria tested. In the all experiments, toluene and m + p- xylenes were better removed than the other BTEXs. No intermediates of biodegradation were detected. Biosurfactant production was observed by culture techniques. In addition, 3-hydroxy fatty acids, important in biosurfactant production, were observed by FAME analysis. The test results indicate that the bacteria could contribute to bioremediation of aromatic hydrocarbon pollution.     

Substrate interactions during the biodegradation of benzene,toluene, ethylbenzene,and xylene (BTEX) hydrocarbons by the fungus Cladophialophora sp. strain T1

The soil fungus Cladophialophora sp. strain T1 (= ATCC MYA-2335) was capable of growth on a model water-soluble fraction of gasoline that contained all six BTEX components (benzene, toluene, ethylbenzene, and the xylene isomers). Benzene was not metabolized, but the alkylated benzenes (toluene, ethylbenzene, and xylenes) were degraded by a combination of assimilation and cometabolism. Toluene and ethylbenzene were used as sources of carbon and energy, whereas the xylenes were cometabolized to different extents. o-Xylene and m-xylene were converted to phthalates as end metabolites; p-xylene was not degraded in complex BTEX mixtures but, in combination with toluene, appeared to be mineralized. The metabolic profiles and the inhibitory nature of the substrate interactions indicated that toluene, ethylbenzene, and xylene were degraded at the side chain by the same monooxygenase enzyme. Our findings suggest that soil fungi could contribute significantly to bioremediation of BTEX pollution.