Degradation of polycyclic aromatic hydrocarbons by an immobilized mixed bacterial culture

The mixed bacterial culture MK1 was capable of degrading a wide spectrum of aromatic compounds both as free and as immobilized cells. By offering anthracene oil or a defined mixture of phenol, naphthalene, phenanthrene, anthracene and pyrene (in concentrations of 0.1–0.2 mm, respectively) as sources of carbon and energy, a specific degradation pattern correlating with the condensation degree was observed. Regarding the defined mixture of aromatic hydrocarbons, complete metabolism was reached for phenol (0.1 mm) after 1 day, for naphthalene (0.1 mm) after 2 days and for phenanthrene (0.1 mm) after 15 days of cultivation. The conversion of anthracene (0.1 mm) and pyrene (0.1 mm) resulted in minimal residual concentrations, analogous to fluoranthene and pyrene of the anthracene oil (0.1%). Maximal total degradation for the tricyclic compounds dibenzofurane, fluorene, dibenzothiophene, phenanthrene and anthracene of the anthracene oil (0.1%) occurred after 5 days. In general, a significant metabolisation of the tetracyclic aromatic hydrocarbons fluoranthene and pyrene was observed after the degradation of phenol, naphthalene and most of the tricyclic compounds. Doubling the start concentrations of the polycyclic aromatic hydrocarbons effected higher degradation rates. Cell growth occurred simultaneously with the conversion of phenol, naphthalene and the tricyclic compounds. The immobilized cells showed stable growth and, compared to freely suspended cells, the same degradation sequence as well as an equivalent degradation potential — even in a model soil system. Correspondence to: I. Wiesel     

Degradation of phenanthrene,fluorene and fluoranthene by pure bacterial cultures

Summary Bacterial mixed cultures able to degrade the polycyclic aromatic hydrocarbons (PAH) phenanthrene, fluorene and fluoranthene, were obtained from soil using conventional enrichment techniques. From these mixed cultures three pure strains were isolated:Pseudomonas paucimobilis degrading phenanthrene;P. vesicularis degrading fluorene andAlcaligenes denitrificans degrading fluoranthene. The maximum rates of PAH degradation ranged from 1.0 mg phenanthrene/ml per day to 0.3 mg fluoranthene/ml per day at doubling times of 12 h to 35 h for growth on PAH as sole carbon source. The protein yield during PAH degradation was about 0.25 mg/mg C for all strains. Maximum PAH oxidation rates and optimum specific bacterial growth were obtained near pH 7.0 and 30°C. After growth entered the stationary phase, no dead end-products of PAH degradation could be detected in the culture fluid.     

乳白耙齿菌F17对单一和复合多环芳烃的降解差异解析

[目的] 针对菲、蒽、荧蒽多环芳烃（PAHs）污染物,利用乳白耙齿菌F17,研究单一和复合PAHs污染物的生物降解规律。[方法] 采用气相色谱-质谱法（GC-MS）分析降解过程中PAHs的浓度,并采用准一级反应动力学模型对降解结果进行拟合。[结果] 对于单一PAHs,第15天时菲、蒽、荧蒽的降解率由高到低依次为菲（97.8%） > 蒽（89.3%） > 荧蒽（81.5%）。菲、蒽和荧蒽的降解过程具有准一级反应动力学特征,菲的生物降解速率最快,其次是蒽,荧蒽的降解速率最慢。与单一PAHs的降解相比,在复合PAHs的降解过程中,乳白耙齿菌F17的生长和锰过氧化物酶的合成均表现出不同的特征。此外,水溶性极可能是复合污染物降解的重要控制因子,三者水溶性为：菲 > 荧蒽 > 蒽。因此,在菲或荧蒽加入条件下,微生物能优先降解这些污染物,抑制了污染物蒽的降解;同时,蒽或菲的存在对荧蒽的降解也有抑制作用;然而外源加入水溶性较差的蒽和荧蒽,则对菲的生物降解无显著影响。[结论] 复合PAHs的生物降解主要表现为相互竞争的特点,通过GC-MS分析了PAHs的生物降解途径。     

Degradation of pyrene byRhodococcus sp. UW1

Summary A Rhodococcus species, designated strain UW1, was isolated from contaminated soil using conventional enrichment and isolation techniques. The isolate was able to use pyrene as sole source of carbon and energy; it mineralized 72% of the pyrene within 2 weeks. During growth a metabolite was detected in the culture fluid and further characterized by UV- and mass spectrometry. There is evidence that this metabolite resulted from a recyclization of the direct meta-ring-fission product of pyrene after dihydroxylation in either the 1,2- or 4,5-position. At pH 7.0 and 30°C Rhodococcus sp. UW1 showed a maximum degradation rate of 0.08 mg pyrene/ml per day, while growing with a doubling time of 30 h. The activity of the initial dioxygenase system was characterized by measuring the oxygen-consumption rates of pyrene-induced resting cells, the maxima of which occurred at pH 7.2 and 45°C. Rhodococcus sp. UW1 could also use phenathrene, anthracene, fluoranthene and chrysene as sole sources of carbon and energy, whereas naphthalene, dibenzofuran, fluorene and dibenzothiophene were only co-metabolized. Offprint requests to: U. Walter     

Influence of growth medium on cometabolic degradation of polycyclic aromatic hydrocarbons by <Emphasis Type="Italic">Sphingomonas</Emphasis> sp. strain PheB4

The influence of growth medium on cometabolic degradation of polycyclic aromatic hydrocarbons (PAHs) was investigated when Sphingomonas sp. strain PheB4 isolated from surface mangrove sediments was grown in either phenanthrene-containing mineral salts medium (PMSM) or nutrient broth (NB). The NB-grown culture exhibited a more rapid cometabolic degradation of single and mixed non-growth substrate PAHs compared to the PMSM-grown culture. The concentrations of PAH metabolites were also lower in NB-grown culture than in PMSM-grown culture, suggesting that NB-grown culture removed metabolites at a faster rate, particularly, for metabolites produced from cometabolic degradation of a binary mixture of PAHs. Cometabolic pathways of single PAH (anthracene, fluorene, or fluoranthene) in NB-grown culture showed similarity to that in PMSM-grown culture. However, cometabolic pathways of mixed PAHs were more diverse in NB-grown culture than that in PMSM-grown culture. These results indicated that nutrient rich medium was effective in enhancing cometabolic degradation of mixed PAHs concomitant with a rapid removal of metabolites, which could be useful for the bioremediation of mixed PAHs contaminated sites using Sphingomonas sp. strain PheB4.     

Metabolism of fluoranthene by Mycobacterium sp. strain AP1

The pyrene-degrading Mycobacterium strain AP1 was found to utilize fluoranthene as a sole source of carbon and energy. Identification of metabolites formed from fluoranthene (by growing cells and washed-cell suspensions), the kinetics of metabolite accumulation, and metabolite-feeding studies all indicated that strain AP1 oxidizes fluoranthene using three alternative routes. The first route is initiated by dioxygenation at C-7 and C-8 and, following meta cleavage and pyruvate release, produces a hydroxyacenaphthoic acid that is decarboxylated to acenaphthenone (V). Monooxygenation of this ketone to the quinone and subsequent hydrolysis generates naphthalene-1,8-dicarboxylic acid (IV), which is further degraded via benzene-1,2,3-tricarboxylic acid (III). A second route involves dioxygenation at C-1 and C-2, followed by dehydrogenation and meta cleavage of the resulting diol. A two-carbon fragment excision of the meta cleavage product yields 9-fluorenone-1-carboxylic acid (II), which appears to undergo angular dioxygenation and further degradation to produce benzene-1,2,3-tricarboxylic acid (III), merging this route with the 7,8-dioxygenation route. Decarboxylation of benzene-1,2,3-tricarboxylic acid to phthalate (VIII), as well as further oxidation of the latter, would connect both routes with the central metabolism. The identification of Z-9-carboxymethylenefluorene-1-carboxylic acid (I) suggests a third route for fluoranthene degradation involving dioxygenation at C-2, C-3, and ortho cleavage. There is no evidence of any further degradation of this compound.     

Phenanthrene stimulates the degradation of pyrene and fluoranthene by <Emphasis Type="Italic">Burkholderia</Emphasis> sp. VUN10013

Pyrene and fluoranthene, when supplied as the sole carbon source, were not degraded by Burkholderia sp. VUN10013. However, when added in a mixture with phenanthrene, both pyrene and fluoranthene were degraded in liquid broth and soil. The amounts of pyrene and fluoranthene in liquid media (initial concentrations of 50 mg l⁻¹ each) decreased to 42.1% and 41.1%, respectively, after 21 days. The amounts of pyrene and fluoranthene in soil (initial concentrations of 75 mg kg⁻¹ dry soil each) decreased to 25.8% and 12.1%, respectively, after 60 days. None of the high molecular weight (HMW) polycylic aromatic hydrocarbons (PAHs) tested adversely affected phenanthrene degradation by this bacterial strain and the amount of phenanthrene decreased rapidly within 3 and 15 days of incubation in liquid broth and soil, respectively. Anthracene also stimulated the degradation of pyrene or fluoranthene by Burkholderia sp. VUN10013, but to a lesser extent than phenanthrene. The extent of anthracene degradation decreased in the presence of these HMW PAHs.     

Biotransformation of the high‐molecular weight polycyclic aromatic hydrocarbon (PAH) benzo[k]fluoranthene by Sphingobium sp. strain KK22 and identification of new products of non‐alternant PAH biodegradation by liquid chromatography electrospray ionization tandem mass spectrometry

A pathway for the biotransformation of the environmental pollutant and high‐molecular weight polycyclic aromatic hydrocarbon (PAH) benzo[k]fluoranthene by a soil bacterium was constructed through analyses of results from liquid chromatography negative electrospray ionization tandem mass spectrometry (LC/ESI(–)‐MS/MS). Exposure of Sphingobium sp. strain KK22 to benzo[k]fluoranthene resulted in transformation to four‐, three‐ and two‐aromatic ring products. The structurally similar four‐ and three‐ring non‐alternant PAHs fluoranthene and acenaphthylene were also biotransformed by strain KK22, and LC/ESI(–)‐MS/MS analyses of these products confirmed the lower biotransformation pathway proposed for benzo[k]fluoranthene. In all, seven products from benzo[k]fluoranthene and seven products from fluoranthene were revealed and included previously unreported products from both PAHs. Benzo[k]fluoranthene biotransformation proceeded through ortho‐cleavage of 8,9‐dihydroxy‐benzo[k]fluoranthene to 8‐carboxyfluoranthenyl‐9‐propenic acid and 9‐hydroxy‐fluoranthene‐8‐carboxylic acid, and was followed by meta‐cleavage to produce 3‐(2‐formylacenaphthylen‐1‐yl)‐2‐hydroxy‐prop‐2‐enoic acid. The fluoranthene pathway converged with the benzo[k]fluoranthene pathway through detection of the three‐ring product, 2‐formylacenaphthylene‐1‐carboxylic acid. Production of key downstream metabolites, 1,8‐naphthalic anhydride and 1‐naphthoic acid from benzo[k]fluoranthene, fluoranthene and acenaphthylene biotransformations provided evidence for a common pathway by strain KK22 for all three PAHs through acenaphthoquinone. Quantitative analysis of benzo[k]fluoranthene biotransformation by strain KK22 confirmed biodegradation. This is the first pathway proposed for the biotransformation of benzo[k]fluoranthene by a bacterium.     

糙皮侧耳和鞘脂菌NS7对多环芳烃污染土壤的生物强化与协同作用

【背景】真菌和细菌被认为在多环芳烃污染土壤生物修复过程中发挥协同作用,目前在真实土壤体系中开展真菌-细菌协同降解研究较少。【目的】研究真菌和细菌对不同种类多环芳烃降解的差异及对蒽和苯并[a]蒽的生物强化与协同作用。【方法】选用多环芳烃降解真菌和细菌各一株,在液体纯培养体系下分析它们对不同种类多环芳烃降解的差异,在土壤体系中采用放射性同位素示踪技术研究2种微生物对蒽和苯并[a]蒽的生物强化与协同作用。【结果】供试细菌鞘脂菌NS7能够很好地降解低环种类多环芳烃,以蒽作为唯一碳源时可以将其完全降解,在复合污染条件下对菲、蒽、荧蒽、芘等降解效果突出(>90%),对苯并[a]芘降解效果较差(9.76%)。相比而言,供试真菌糙皮侧耳菌对苯并[a]芘具有更好的降解效果(21.18%),对低环多环芳烃降解效果明显不如降解菌NS7。在自然土壤中,蒽和苯并[a]蒽具有明显不同的矿化效率,分别为18.61%和4.28%,在蒽污染土壤中加入鞘脂菌NS7并未显著提高蒽的矿化率(P>0.05),相比而言,苯并[a]蒽污染土壤中加入糙皮侧耳显著提高了污染物矿化效率(2.24倍),表明真菌和细菌在土壤环境...     

Biodegradation of mixtures of chlorophenoxyalkanoic acid herbicides by Alcaligenes denitrificans

An Alcaligenes denitrificans strain able to degrade (R)-2-(2-methyl-4-chlorophenoxy)propionic acid [(R)-MCPP, mecoprop] was assessed for its ability to utilise a range of chlorophenoxyalkanoic acid herbicides in single, binary, tertiary and quaternary combinations in batch culture. Degradation rates were rapid with single growth substrates; complete degradation occurred within 29 h for 2,4-dichlorophenoxyacetic acid (2,4-D), 43 h for 4-chloro-2-methylphenoxyacetic acid (MCPA) and 50 h for (R)-MCPP, respectively. After 20 h, the degradation of (RS)-2-(2,4-dichlorophenoxy)propionic acid [(RS)-2,4-DP] had ceased, with only the (R)-enantiomer being degraded. In binary combination, 2,4-D and MCPP degraded within 55 h. Degradation rates decreased when herbicides were added in tertiary and quaternary combinations. Thus, at the whole cell level, catalysis of closely related herbicides is likely to be facilitated by diverse enzymatic activity in A. denitrificans. Journal of Industrial Microbiology & Biotechnology (2000) 25, 255–259. Received 16 April 2000/ Accepted in revised form 07 August 2000     

Degradation of pyrene by Mycobacterium flavescens

 A strain of Mycobacterium flavescens was isolated from polluted sediments. It was capable of utilizing pyrene as a sole source of carbon and energy. When pyrene was supplied as a suspension at 50 μg/ml, the generation time was 9.6 h and the rate of pyrene utilization was 0.56 μg ml^-1 day^-1. In addition to pyrene, the strain could mineralize phenanthrene (17.7%) and fluoranthene (17.9%), but failed to mineralize naphthalene, chrysene, anthracene, fluorene, acenaphthene and benzo[a]pyrene, as determined by recovery of radiolabeled CO₂ in incubations conducted for 2 weeks under growth conditions. Metabolites produced during growth on pyrene were detected and characterized by HPLC and GC-MS. The product of initial ring oxidation, 4,5-dihydroxy-4,5-dihydropyrene was identified, as well as ring-fission products including 4-phenanthroic acid, phthalic acid, and 4,5-phenanthrenedioic acid. Received: 3 October 1995/Received last revision: 1 April 1996/Accepted: 15 April 1996     

Isolation and characterization of a fluoranthene-utilizing strain of Pseudomonas paucimobilis

A soil bacterium capable of utilizing fluoranthene as the sole source of carbon and energy for growth was purified from a seven-member bacterial community previously isolated from a creosote waste site for its ability to degrade polycyclic aromatic hydrocarbons. By standard bacteriological methods, this bacterium was characterized taxonomically as a strain of Pseudomonas paucimobilis and was designated strain EPA505. Utilization of fluoranthene by strain EPA 505 was demonstrated by increase in bacterial biomass, decrease in aqueous fluoranthene concentration, and transient formation of transformation products in liquid cultures where fluoranthene was supplied as the sole carbon source. Resting cells grown in complex medium showed activity toward anthraquinone, benzo[b]fluorene, biphenyl, chrysene, and pyrene as demonstrated by the disappearance of parent compounds or changes in their UV absorption spectra. Fluoranthene-grown resting cells were active against these compound as well as 2,3-dimethylnaphthalene, anthracene, fluoranthene, fluorene, naphthalene, and phenanthrene. These studies demonstrate that organic compounds not previously reported to serve as growth substrates can be utilized by axenic cultures of microorganisms. Such organisms may possess novel degradative systems that are active toward other compounds whose biological degradation has been limited because of inherent structural considerations or because of low aqueous solubility.     

Isolation and characterization of a fluoranthene-utilizing strain of Pseudomonas paucimobilis.

A soil bacterium capable of utilizing fluoranthene as the sole source of carbon and energy for growth was purified from a seven-member bacterial community previously isolated from a creosote waste site for its ability to degrade polycyclic aromatic hydrocarbons. By standard bacteriological methods, this bacterium was characterized taxonomically as a strain of Pseudomonas paucimobilis and was designated strain EPA505. Utilization of fluoranthene by strain EPA 505 was demonstrated by increase in bacterial biomass, decrease in aqueous fluoranthene concentration, and transient formation of transformation products in liquid cultures where fluoranthene was supplied as the sole carbon source. Resting cells grown in complex medium showed activity toward anthraquinone, benzo[b]fluorene, biphenyl, chrysene, and pyrene as demonstrated by the disappearance of parent compounds or changes in their UV absorption spectra. Fluoranthene-grown resting cells were active against these compound as well as 2,3-dimethylnaphthalene, anthracene, fluoranthene, fluorene, naphthalene, and phenanthrene. These studies demonstrate that organic compounds not previously reported to serve as growth substrates can be utilized by axenic cultures of microorganisms. Such organisms may possess novel degradative systems that are active toward other compounds whose biological degradation has been limited because of inherent structural considerations or because of low aqueous solubility.     

Effect of surfactants on fluoranthene degradation by <Emphasis Type="Italic">Pseudomonas alcaligenes</Emphasis> PA-10

Two surfactants, Tween 80 and JBR, were investigated for their effect on fluoranthene degradation by a Pseudomonad. Both surfactants enhanced fluoranthene degradation by Pseudomonas alcaligenes PA-10 in shake flask culture. This bacterium was capable of utilising the synthetic surfactant and the biosurfactant as growth substrates and the critical micelle concentration of neither compound inhibited bacterial growth. The biosurfactant JBR significantly increased polycyclic aromatic hydrocarbon (PAH) desorption from soil. Inoculation of fluoranthene-contaminated soil microcosms with P. alcaligenes PA-10 resulted in the removal of significant amounts (45 ± 5%) of the PAH after 28 days compared to an uninoculated control. Addition of the biosurfactant increased the initial rate of fluoranthene degradation in the inoculated microcosm. The presence of a lower molecular weight PAH, phenanthrene, had a similar effect on the rate of fluoranthene removal.     

Effect of surfactants and identification of metabolites on the biodegradation of fluoranthene by basidiomycetes fungal isolate Armillaria sp. F022

The effects of structure and concentration of surfactants on the biodegradation of fluoranthene, a three rings polycyclic aromatic hydrocarbon in the aqueous phase, as well as their effects on the biodegradation and enzyme activity were investigated. The toxicity ranking of studied surfactants is: non-ionic Tween 80 <anionic sodium dodecyl sulfate <cationic Tetradecyltrimethylammonium bromide. The maximum growth of Armillaria sp. F022 (>4,500 mg/L) was showed by Tween 80 (10 mg/L) culture, manifesting that the non-ionic surfactant present in the culture were beneficial to the fungal growth. Laccase showed the highest enzymes activity in all surfactants culture. Non-ionic Tween 80 showed a significant result for laccase activity (1,902 U/L) in the Armillaria sp. F022 culture. The increased enzymes cumulative activity may stem directly from the rising fluoranthene biodegradability as addition of appropriate surfactants. The biotransformation of fluoranthene was greatly improved by Tween 80, and totally fluoranthene degradation was obtained as Tween 80 was 10 mg/L. Two fluoranthene metabolites were isolated from the culture medium and analyzed by a thin layer chromatography, UV visible spectrometer and gas chromatography–mass spectrometry (GC–MS). The oxidation of fluoranthene is initiated by oxygenation at the C-2,3 positions resulting 9-fluorenone. At the end of experiment, one metabolite was detected in the culture extract and identified as phthalic acid. Evidently, Armillaria sp. F022 seems efficient, high effective and deserves further application on the enhanced bioremediation technologies for the treatment of fluoranthene-contaminated soil.     

Degrading ability of oligocyclic aromates by <Emphasis Type="Italic">Phanerochaete sordida</Emphasis> selected <Emphasis Type="Italic">via</Emphasis> screening of white rot fungi

Seventy-nine white rot strains were screened to determine if they had the potential for use in the degradation of oligocyclic aromates (PAHs) by measuring their dye-decoloration rate. Fourteen strains that were selected based on their dye-decoloration rate were then evaluated for the ability to tolerate various levels of PAHs spiked in agar medium. The ability of white rot fungi to degrade 3- or 4-ring PAHs (anthracene, phenanthrene, fluoranthene, pyrene) was determined. Two strains of Phanerochaete sordida (KUC8369, KUC8370) were possible PAHs degraders, degrading a significantly greater amount of phenanthrene and fluoranthene than the culture collection strain P. chrysosporium (a known PAHs degrader). The production of manganese peroxidase, the only extracellular ligninolytic enzyme detected during the cultivation, was evaluated.     

Thiodiglycol Metabolism in Alcaligenes xylosoxydans subsp. denitrificans

The investigation of the degradation of thiodiglycol (the major product of mustard gas hydrolysis) by Alcaligenes xylosoxydans subsp. denitrificans strain TD2 showed that thiodiglycol is metabolized through the oxidation of its primary alcohol groups and the subsequent cleavage of C–S bonds in the intermediate products, thiodiglycolic and thioglycolic acids. The end products of these reactions are SO₄ ^2– ions and acetate, the latter being involved in the central metabolism of strain TD2. The oxidation of the sulfur atom gives rise to diglycolsulfoxide, which is recalcitrant to further microbial degradation. Based on the data obtained, a metabolic pathway of thiodiglycol transformation by A. xylosoxydans subsp. denitrificans strain TD2 is proposed.     

Metabolism of fluoranthene by mycobacterial strains isolated by their ability to grow in fluoranthene or pyrene

Mycobacterium sp. strains CP1, CP2, CFt2 and CFt6 were isolated from creosote-contaminated soil due to their ability to grow in pyrene (CP1 and CP2) or fluoranthene (CFt2 and CFt6). All these strains utilized fluoranthene as a sole source of carbon and energy. Strain CP1 exhibited the best growth, with a cellular assimilation of fluoranthene carbon of approximately 45%. Identification of the metabolites accumulated during growth in fluoranthene, the kinetics of metabolites, and metabolite feeding studies, indicated that all these isolates oxidized fluoranthene by the following two routes: the first involves dioxygenation at C-1 and C-2, meta cleavage, and a 2-carbon fragment excision to produce 9-fluorenone-1-carboxylic acid. An angular dioxygenation of the latter yields cis-1,9a-dihydroxy-1-hydrofluorene-9-one-8-carboxylic acid, which is further degraded via 8-hydroxy-3,4-benzocoumarin-1-carboxylic acid, benzene-1,2,3-tricarboxylic acid, and phthalate; the second route involves dioxygenation at C-2 and C-3 and ortho cleavage to give Z-9-carboxymethylenefluorene-1-carboxylic acid. In addition, the pyrene-degrading strains CP1 and CP2 possess a third route initiated by dioxygenation at positions C-7 and C-8, which—following meta cleavage, an aldolase reaction, and a C₁-fragment excision—yields acenaphthenone. Monooxygenation of this ketone to the corresponding quinone, and its subsequent hydrolysis, produces naphthalene-1,8-dicarboxylic acid. The results obtained in this study not only complete and confirm the three fluoranthene degradation routes previously proposed for the pyrene-degrading strain Mycobacterium sp. AP1, but also suggest that such routes represent general microbial processes for environmental fluoranthene removal.     

Enumeration and characterization of the soil microflora from hydrocarbon-contaminated soil sites able to mineralize polycyclic aromatic hydrocarbons (PAH)

The use of a plate screening technique allowed the direct isolation and quantification of polycylic aromatic hydrocarbon (PAH)-degrading bacteria from different soil sites. Bacteria that were able to grow on anthracene, phenanthrene, fluoranthene or pyrene as a sole carbon source were found with numbers between 10³ and 10⁵ colony-forming units (cfu)/g of soil dry weight, but only in samples that originated from PAH-contaminated sites. No isolates were found that could grow on perylene, triphenylene, benzo(a)pyrene or chrysene as sole carbon source. Bacteria that had been selected on the same PAH substrate showed a related degradation pattern for both other PAH and oil compounds and carbohydrate substrates even if they had been collected at distant soil sites. Based on these findings the isolates could be clustered into four different catabolic and taxonomic similarity groups. Taxonomic determination of representative isolates suggested that nocardioform actinomycetes of the genera Mycobacterium, Rhodococcus and Gordona represented a major part of the soil microflora able to mineralize PAH. Three new isolates able to grow on anthracene, pyrene or fluoranthene as the sole carbon source, respectively, have been isolated and identified (Sphingomonas paucimobilis BA2, Gordona sp. BP9, Mycobacterium sp. VF1). The ubiquitous presence of a potent and versatile mineralizing microflora in PAH-contaminated soils indicated that the microflora is not the limiting factor for the degradation of PAH with up to four rings.     

Kinetics of Polycyclic Aromatic Hydrocarbon (PAH) Degradation in Long-term Polluted Soils during Bioremediation

Bioremediation experiments with ten different soil samples from former industrial sites which were long-term polluted with polycyclic aromatic hydrocarbons (PAHs) were carried out using outdoor pot trials. The degradation of 15 PAHs according to the US EPA was investigated for 168 weeks through repeated soil sampling and determination of the total PAH concentration. On average, degradation was largest for acenaphthene (88%; 63 to 99%) and smallest for anthracene (22%; no significant degradation to 89%). For most of the PAH single substances, degradation kinetics were characterised by a first initial phase of fast degradation. In a subsequent second phase, degradation diminished and residual PAH concentrations were approached within 168 weeks, resulting in a similar PAH pattern in the ten soil samples. Degradation kinetics was calculated through the selection of the appropriate differential rate equation from a set of seven equations. Kinetics of PAH degradation was best fitted by single and two coupled first order exponential equations with median R2 of 0.71 (0.01 to 1.00). Degradation rate constants of the rapid phase (k ₁) ranged from 0.05×10⁻² week⁻¹ for benzo[k]fluoranthene to 18.3 week⁻¹ for naphthalene and for the subsequent slow degradation phase (k ₂) they ranged from 0.01×10⁻² week⁻¹ for benzo[a]anthracene to 2.3×10⁻² week⁻¹ for fluoranthene. Degradation was governed by desorption and diffusion processes of different rates, while microbial activity did not influence the kinetics. Median disappearance times (DT₅₀) ranged from 6.1 weeks for naphthalene to 522 weeks for benzo[k]fluoranthene. With the exception of the 6-ring PAHs dibenzo[ah]anthracene and indeno[1,2,3-cd]pyrene, this sequence followed the PAHs’ degree of condensation. The total initial PAH concentration and the residual concentration were correlated with R2 of 0.69, with larger initial PAH concentrations leading to larger residual concentrations and degradation rates.