Action of a Fluoranthene-Utilizing Bacterial Community on Polycyclic Aromatic Hydrocarbon Components of Creosote

Cultures enriched by serial transfer through a mineral salts medium containing fluoranthene were used to establish a stable, seven-member bacterial community from a sandy soil highly contaminated with coal tar creosote. This community exhibited an ability to utilize fluoranthene as the sole carbon source for growth, as demonstrated by increases in protein concentration and changes in absorption spectra when grown on fluoranthene in liquid culture. Biotransformation of other polycyclic aromatic hydrocarbons (PAHs) was verified by demonstrating their disappearance from an artificial PAH mixture by capillary gas chromatography. When grown on fluoranthene as the sole carbon source and subsequently exposed to fluoranthene plus 16 additional PAHs typical of those found in creosote, this community transformed all PAHs present in this defined mixture. After 3 days of incubation, 13 of the original 17 PAH components were degraded to levels below the limit of detection (10 ng/liter). Continued incubation resulted in extensive degradation of the remaining four compounds. The ability of this community to utilize a high-molecular-weight PAH as the sole carbon source, in conjunction with its ability to transform a diverse array of PAHs, suggests that it may be of value in the bioremediation of environments contaminated with PAHs, such as those impacted by creosote.     

Isolation of phenanthrene-degrading bacteria and characterization of phenanthrene metabolites

Three aerobic bacterial consortia GY2, GS3 and GM2 were enriched from polycyclic aromatic hydrocarbon-contaminated soils with water-silicone oil biphasic systems. An aerobic bacterial strain utilizing phenanthrene as the sole carbon and energy source was isolated from bacterial consortium GY2 and identified as Sphingomonas sp. strain GY2B. Within 48 h and at 30°C the strain metabolized 99.1% of phenanthrene (100 mg/l) added to batch culture in mineral salts medium and the cell number increased by about 40-fold. Three metabolites 1-hydroxy-2-naphthoic acid, 1-naphthol and salicylic acid, were identified by gas chromatographic mass spectrometry and UV–visible spectroscopy analysis. A degradation pathway was proposed based on the identified metabolites. In addition to phenanthrene, strain GY2B could use other aromatic compounds such as naphthalene, 2-naphthol, salicylic acid, catechol, phenol, benzene and toluene as a sole source of carbon and energy.     

Phylogenetic and physiological comparisons of PAH-degrading bacteria from geographically diverse soils

The diversity of bacteria isolated from creosote- contaminated soils in the United States, Norway, and Germany was determined by comparing their ability to degrade polycyclic aromatic hydrocarbons (PAHs), their phospholipid ester-linked fatty acid (GC-FAME) profiles, sole carbon source utilization patterns (Biolog assays (Use of trade names or specific products does not imply endorsement by the U.S. EPA.), and 16S rRNA sequences. Bacteria were initially obtained by enrichment with phenanthrene and fluoranthene. Many were capable of degrading a broad range of the PAHs found in creosote. Phenanthrene- or fluoranthene- degraders were abundant in most of the soils tested. Several of the fluoranthene-degrading isolates clustered with Sphingomonas (formerly Pseudomonas) paucimobilis strain EPA505 in the GC-FAME and Biolog analyses and three of the isolates examined by 16S rRNA sequence comparisons showed a close relationship with Sphingomonas. In addition, the Sphingomonas strains showed the most extensive degradation of 4- & 5-ring PAHs in creosote. Burkholderia cepacia strains isolated on phenanthrene from PAH-contaminated soils had limited ability to attack higher molecular weight PAHs either individually or in creosote. Thus, PAH degradation capabilities appeared to be associated with members of certain taxa, independent of the origin of the soils from which the bacteria were isolated.     

Bacterial degradation of low concentrations of phenanthrene and inhibition by naphthalene

Phenanthrene-degrading bacteria were isolated from enrichment cultures of soils contaminated with creosote and jet fuel. The isolates from the creosote enrichments were classified by fatty acid methyl ester profiles as Acidovorax delafieldii and Sphingomonas paucimobilis; the bacterium from the jet fuel-contaminated soil was not identified and was designated strain JFD 11. All three isolates used phenanthrene as a sole carbon and energy source, and two of the isolates used fluoranthene as a sole carbon and energy source. Anthracene and fluorene were cometabolized by all three strains, but pyrene was not transformed. Naphthalene inhibited all of the strains, and 28-h cultures of A. delafieldii were inhibited by naphthalene concentrations as low as 5 ppm. Short-term degradation experiments were undertaken with center-well flasks and concentrations of phenanthrene ranging from 1.2 to 12.0 m. Since initial degradation rates were not a function of phenanthrene concentration, it was inferred that the half-saturation constants were less than the lowest phenanthrene concentration tested. Correspondence to: C.E. Cemiglia.     

多环芳烃降解菌的筛选、鉴定及降解特性

【目的】多环芳烃(PAHs)是一类普遍存在于环境中且具有高毒性的持久性有机污染物,高效降解菌的筛选对利用生物修复技术有效去除环境中的多环芳烃具有重要意义。研究拟从供试菌株中筛选多环芳烃高效降解菌,并分析其降解特性,为多环芳烃污染环境的微生物修复提供资源保障和科学依据。【方法】采用平板法从25株供试菌株中筛选出以菲和芘为唯一碳源和能源的高效降解菌,经16S rRNA基因序列进行初步鉴定,通过单因素实验法分析其在液体培养基中的降解特性。【结果】筛选出的3株多环芳烃高效降解菌SL-1、02173和02830经16S rRNA基因序列分析,02173和02830分别与假单胞菌属中的Pseudomonas alcaliphila和Pseudomonas corrugate同源性最近,SL-1为本课题组发表新类群Rhizobium petrolearium的模式菌株;降解实验表明,菌株SL-1 3 d内对单一多环芳烃菲(100 mg/L)和芘(50 mg/L)的降解率分别达到100%和48%,5 d后能够降解74%的芘;而其3 d内对混合PAHs中菲和芘的降解率分别为75.89%和81.98%。菌株02173和02830 3 d内对混合多环芳烃中萘(200 mg/L)、芴(50 mg/L)、菲(100 mg/L)和芘(50 mg/L)的降解率均分别超过97%。【结论】筛选出的3株PAHs降解菌SL-1、02173和02830不仅可以高效降解低分子量PAHs,还对高分子量PAHs具有很好的降解潜力。研究表明,由于共代谢作用低分子量多环芳烃可促进高分子量多环芳烃的降解,而此时低分子量多环芳烃的降解将受到抑制。     

Biodegrading of pyrene by a newly isolated Pseudomonas putida PL2

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic compounds derived from natural sources and anthropogenic processes, which have been recommended as priority pollutants. Degradation of PAHs in the environment is becoming more necessary and urgent. In the current study, strain PL2, which is capable of growing aerobically on pyrene (PYR) as the sole carbon source, was isolated from hydrocarbons-contaminated soil and then identified as Pseudomonas putida by morphological and physiological characteristics as well as 16S rDNA sequence. The strain PL2 was able to degrade 50.0% of the pyrene at 28°C within 6 days in the presence of 50 mg/L pyrene, while the strain PL2 degraded 50.0% of the pyrene within 2 days when a solution of 50 mg/L pyrene and 50 mg/L phenanthrene was used. In addition, phenanthrene was shown to increase the biodegradation efficiency of pyrene by the strain PL2. The order of degradation by the strain PL2 was pH 6.0 > pH 7.0 > pH 5.0 > pH 8.0. The degradation rate of PYR in the soil by the strain PL2 reached 70.0% at the 10^th day. The dynamics of PYR degradation in soil by PL2 was fit to the first order model and the strain PL2 was shown to efficiently degrade PYR in soil. The current study showed that P. putida PL2 was a novel bacterium that could degrade pyrene and holds great promise for use in PAHs bioremediation in soil.     

A phenanthrene-degrading strain Sphingomonas sp. GY2B isolated from contaminated soils

This study systematically characterized an aerobic bacterial strain Sphingomonas sp. GY2B for biotransformation of phenanthrene. The strain was isolated from soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and was shown to efficiently use phenanthrene as the sole carbon and energy source. The antibiotics discs susceptibility test revealed that the bacterium was susceptible to some commonly used antibiotics, such as cefuroxime, chloramphenicol, erythromycin and tetracycline. It showed better growth at pH 7.4 and 30 °C and in a mineral salts medium (MSM) with phenanthrene at 100 mg L⁻¹ as the substrate. The results indicated that 99.8% of the substrate had been degraded and that salicylate route was likely the metabolic pathway. When added as the second organic chemical, glucose could enhance the bacterial growth at low concentration (10–200 mg L⁻¹), but could inhibit cell growth at high concentration (>500 mg L⁻¹). Further study showed that strain GY2B could also use naphthalene, phenol, 1-hydroxy-2-naphthoic acid, 2-naphthol, salicylic acid and catechol as the sole carbon and energy source, but did not grow on 1-naphthol which could be co-metabolized in the present of phenanthrene or 1-hydroxy-2-naphthoic acid.     

嗜麦芽寡养单胞菌PX1的降解芘特性及定殖效能

为丰富多环芳烃降解菌菌种库、降低农作物的污染风险,本研究对一株可高效降解多环芳烃(PAHs)的植物内生菌进行筛选鉴定,并初步探究其降解途径以及定殖效能。结果表明: 菌株PX1为嗜麦芽寡养单胞菌。该菌株对多环芳烃的降解具有广谱性,7 d几乎可彻底降解PAH无机盐培养基中的萘,在分别含有50.0 mg·L^-1菲、20.0 mg·L^-1芘、20.0 mg·L^-1荧蒽和10.0 mg·L^-1苯并[a]芘的培养体系中,对菲、芘、荧蒽、苯并[a]芘的降解率分别为72.6%、50.7%、31.9%和12.9%。选取芘作为PAHs模型研究菌株PX1的降解特性。酶活性试验表明,芘可诱导菌株PX1体内邻苯二甲酸双加氧酶、邻苯二酚-1,2-双加氧酶和邻苯二酚-2,3-双加氧酶的活性。在芘降解过程中检测到4,5-环氧化芘、4,5-二羟基芘、龙胆酸/原茶儿酸、水杨酸、顺-己二烯二酸/2-羟粘糠酸半醛、顺-2′-羧基苯丙酮酸、1-羟基-2-萘甲酸、水杨醛等中间产物。浸种定殖试验表明,菌株PX1可高效定殖到空心菜和小麦体内,显著促进空心菜和小麦生长,并能够将空心菜、小麦体内及其生长基质中的芘浓度分别降低29.8%～50.7%、52.4%～67.1%和8.0%～15.3%。表明菌株PX1主要通过“水杨酸途径”和“邻苯二甲酸途径”降解芘,且可以定殖到植物体内,促进植物生长。     

Isolation and Characterization of a Mycobacterium Species Capable of Degrading Three- and Four-Ring Aromatic and Aliphatic Hydrocarbons

Mycobacterium sp. strain CH1 was isolated from polycyclic aromatic hydrocarbon (PAH)-contaminated freshwater sediments and identified by analysis of 16S rDNA sequences. Strain CH1 was capable of mineralizing three- and four-ring PAHs including phenanthrene, pyrene, and fluoranthene. In addition, strain CH1 could utilize phenanthrene or pyrene as a sole carbon and energy source. A lag phase of at least 3 days was observed during pyrene mineralization. This lag phase decreased to less than 1 day when strain CH1 was grown in the presence of phenanthrene or fluoranthene. Strain CH1 also was capable of using a wide range of alkanes as sole carbon and energy sources. No DNA hybridization was detected with the nahAc gene probe, indicating that enzymes involved in PAH metabolism are not related to the well-characterized naphthalene dioxygenase gene. DNA hybridization was not detected when the alkB gene from Pseudomonas oleovorans was used under high-stringency conditions. However, there was slight but detectable hybridization under low-stringency conditions. This suggests a distant relationship between genes involved in alkane oxidation.     

Degradation of fluoranthene, pyrene, benz[a]anthracene and dibenz[a,h]anthracene by Burkholderia cepacia

Microbiological analysis of soils from a polycyclic aromatic hydrocarbon (PAH)-contaminated site resulted in the enrichment of five microbial communities capable of utilizing pyrene as a sole carbon and energy source. Communities 4 and 5 rapidly degraded a number of different PAH compounds. Three pure cultures were isolated from community 5 using a spray plate method with pyrene as the sole carbon source. The cultures were identified as strains of Burkholderia ( Pseudomonas ) cepacia on the basis of biochemical and growth tests. The pure cultures (VUN 10 001, VUN 10 002 and VUN 10 003) were capable of degrading fluorene, phenanthrene and pyrene (100 mg l⁻¹) to undetectable levels within 7–10 d in standard serum bottle cultures. Pyrene degradation was observed at concentrations up to 1000 mg l⁻¹. The three isolates were also able to degrade other PAHs including fluoranthene, benz[ a ]anthracene and dibenz[ a , h ]anthracene as sole carbon and energy sources. Stimulation of dibenz[ a , h ]anthracene and benzo[ a ]pyrene degradation was achieved by the addition of small quantities of phenanthrene to cultures containing these compounds. Substrate utilization tests revealed that these micro-organisms could also grow on n -alkanes, chlorinated- and nitro-aromatic compounds.     

Study of the Degradation Activity and the Strategies to Promote the Bioavailability of Phenanthrene by Sphingomonas paucimobilis Strain 20006FA

The present study describes the phenanthrene-degrading activity of Sphingomonas paucimobilis 20006FA and its ability to promote the bioavailability of phenanthrene. S. paucimobilis 20006FA was isolated from a phenanthrene-contaminated soil microcosm. The strain was able to grow in liquid mineral medium saturated with phenanthrene as the sole carbon source, showing high phenanthrene elimination (52.9% of the supplied phenanthrene within 20 days). The accumulation of 1-hydroxy-2-naphthoic acid and salicylic acid as major phenanthrene metabolites and the capacity of the strain to grow with sodium salicylate as the sole source of carbon and energy indicated that the S. paucimobilis 20006FA possesses a complete phenanthrene degradation pathway. However, under the studied conditions, the strain was able to mineralize only the 10% of the consumed phenanthrene. Investigations on the cell ability to promote bioavailability of phenanthrene showed that the S. paucimobilis strain 20006FA exhibited low cell hydrophobicity (0.13), a pronounced chemotaxis toward phenanthrene, and it was able to reduce the surface tension of mineral liquid medium supplemented with phenanthrene as sole carbon source. Scanning electron micrographs revealed that: (1) in suspension cultures, cells formed flocks and showed small vesicles on the cell surface and (2) cells were also able to adhere to phenanthrene crystals and to produce biofilms. Clearly, the strain seems to exhibit two different mechanisms to enhance phenanthrene bioavailability: biosurfactant production and adhesion to the phenanthrene crystals.     

盐碱土壤PAHs 降解菌的筛选鉴定及其降解特性

采用富集培养的方法,从天津大港油田PAHs污染盐碱化土壤中分离出一株能以菲、芘为唯一碳源和能源的优势菌TJB5。经形态观察和16S rDNA序列分析结果表明,该菌株为成团泛菌(Pantoea agglomerans)。采用液体培养的方法,研究了pH、盐度、菲芘的初始浓度对TJB5菌株降解菲芘效果的影响,确定了最佳降解条件。结果表明,该菌对菲、芘的降解具有较广泛的pH、盐度范围和良好的降解效果。在菲、芘浓度分别为50 mg/L、pH 6.8-9.5、盐度2%-3%、温度30°C条件下,接种15 d后菲降解率在93.3%以上,芘降解率在20%以上。     

Cometabolic oxidation of phenanthrene to phenanthrene trans-9,10-dihydrodiol by Mycobacterium strain S1 growing on anthracene in the presence of phenanthrene.

Mycobacterium strain S1, originally described as Rhodococcus strain S1 by chemotaxonomic criteria, was isolated by growth on anthracene, and is unable to use any of nine other polycyclic aromatic compounds as carbon source. Metabolism of phenanthrene during growth on anthracene as sole carbon source results in the accumulation of traces of a dihydrodiol metabolite in the growth medium, which, by comparison with authentic standards, has been tentatively identified as phenanthrene trans-9,10-dihydrodiol. Anthracene metabolites were ruled out on the basis of comparisons with authentic anthracene dihydrodiols from Pseudomonas fluorescens D1 and chemically synthesized anthrols. The original source of phenanthrene for dihydrodiol production was phenanthrene present as a < 1% contaminant in the anthracene used as carbon source. However, addition of further phenanthrene to the anthracene growth medium increased the level of phenanthrene trans-9,10-dihydrodiol formed. Mycobacterium strain S1 also produced phenanthrene trans-9,10-dihydrodiol when grown in a glucose-salts medium in the presence of phenanthrene. This dihydrodiol is a dead-end metabolite, and neither it nor its parent hydrocarbon are able to support the growth of Mycobacterium strain S1. Studies with metyrapone and ancimidol, which did not inhibit growth on anthracene but did inhibit formation of phenanthrene trans-9,10-dihydrodiol, suggest it is likely the product of a cytochrome P450 monooxygenase-like activity.     

Fluorene and phenanthrene uptake by Pseudomonas putida ATCC 17514: kinetics and physiological aspects

Pseudomonas putida ATCC 17514 was used as a model strain to investigate the characteristics of bacterial growth in the presence of solid fluorene and phenanthrene. Despite the lower water-solubility of phenanthrene, P. putida degraded this polycyclic aromatic hydrocarbon (PAH) at a maximum observed rate of 1.4 +/- 0.1 mg L(-1) h(-1), higher than the apparent degradation rate of fluorene, 0.8 +/- 0.07 mg L(-1) h(-1). The role of physiological processes on the biodegradation of these PAHs was analyzed and two different uptake strategies were identified. Zeta potential measurements revealed that phenanthrene-grown cells were slightly more negatively charged (-57.5 +/- 4.7 mV) than fluorene-grown cells (-51.6 +/- 4.9 mV), but much more negatively charged than glucose-grown cells (-26.8 +/- 3.3 mV), suggesting that the PAH substrate induced modifications on the physical properties of bacterial surfaces. Furthermore, protein-to-exopolysaccharide ratios detected during bacterial growth on phenanthrene were typical of biofilms developed under physicochemical stress conditions, caused by the presence of sparingly water-soluble chemicals as the sole carbon and energy source for growth, the maximum value for TP/EPS during growth on phenanthrene (1.9) being lower than the one obtained with fluorene (5.5). Finally, confocal laser microscopy observations using a gfp-labeled derivative strain revealed that, in the presence of phenanthrene, P. putida::gfp cells formed a biofilm on accessible crystal surfaces, whereas in the presence of fluorene the strain grew randomly between the crystal clusters. The results showed that P. putida was able to overcome the lower aqueous solubility of phenanthrene by adhering to the solid PAH throughout the production of extracellular polymeric substances, thus promoting the availability and uptake of such a hydrophobic compound.     

Isolation and characterization of a 2-methylphenanthrene utilizing bacterium: identification of ring cleavage metabolites

A bacterial strain capable of utilizing 2-methylphenanthrene (2-MP) as its sole source of carbon and energy for growth was isolated from creosote contaminated soil. The isolate was identified as a strain of Sphingomonas sp. and was designated strain JS5. Utilization of 2-MP by strain JS5 was demonstrated by an increase in bacterial biomass concomitant with a decrease of 2-MP in liquid mineral medium with this compound as sole source of carbon and energy. Growth yield indicated a 23% assimilation of 2-MP carbon. Washed-cell suspensions of strain JS5 incubated with 2-MP accumulated a major metabolite identified as 1-hydroxy-6-methyl-2-naphtoic acid, according to its UV, mass and NMR spectra, and a minor compound with HPLC R _t and UV spectrum indistinguishable from 5-methylsalicylate. The identification of those metabolites, and the demonstration of 2,3-catechol dioxygenase activity in 2-MP induced cells show that the biodegradation of 2-MP by strain JS5 is initiated via dioxygenation and meta-cleavage of the non-methylated aromatic ring, and then proceeds by reactions similar to those reported for phenanthrene. Incubation of the strain with a MP-containing mixture from a pyrolytic fuel oil demonstrates that strain JS5 also acts on other methylated phenanthrenes. Received: 28 December 1998 / Received revision: 21 June 1999 / Accepted: 27 June 1999     

Bioremediation of Polycyclic Aromatic Hydrocarbons in Creosote-Contaminated Soil by Peniophora incarnata KUC8836

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) are present in products made from creosote, coal tar, and asphalt. When wood pile treated with creosote is placed in soil, PAHs can contaminate it. Creosote has been used for wood preservation in the past and is composed of approximately 85% PAHs and 15% phenolic compounds. PAHs cause harmful effects to humans and the environment because of their carcinogenic and mutagenic properties. White rot fungi can degrade not only lignin, but also recalcitrant organic compounds such as PAHs. Among numerous white rot fungi used in previous studies, four species were selected to degrade PAHs in a liquid medium. From this evaluation of the degradation of PAHs by the four fungal isolates, two species were ultimately selected for the highest rates of removal. Following 2 weeks of incubation with Peniophora incarnata KUC8836, the degradation rates of phenanthrene, fluoranthene, and pyrene were 86.5%, 77.4%, and 82.6%, respectively. Mycoaciella bispora KUC8201 showed the highest degradation rate for anthracene (61.8%). Hence, bioremediation of creosote-contaminated soil with an initial concentration of 229.49 mg kg^?1 PAHs was carried out using the two selected fungi because they could simultaneously degrade 13 more PAHs than the comparison species. More importantly, isolates of P. incarnata KUC8836 were discovered as powerful degraders of PAHs by producing laccase and manganese-dependent peroxidase (MnP), with 1.7- and 1.1-fold higher than the comparison species, respectively. Therefore, the white rot fungus may be proposed for the removal of PAHs and xenobiotic compounds in contaminated environments.     

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.     

Mineralization of phenol and its derivatives by Pseudomonas sp. strain CP4

A Pseudomonas sp. strain, CP4, was isolated that used phenol up to 1.5 g/l as sole source of carbon and energy. Optimal growth on 1.5 g phenol/l was at pH 6.5 to 7.0 and 30°C. Unadapted cells needed 72 h to decrease the chemical oxygen demand (COD) of about 2000 mg/l (from 1 g phenol/l) to about 200 mg/l. Adapted cells, pregrown on phenol, required only 65 h to decrease the COD level to below 100 mg/l. Adaptation of cells to phenol also improved the degradation of cresols. Cell-free extracts of strain CP4 grown on phenol or o-, m- or p-cresol had sp. act. of 0.82, 0.35, 0.54 and 0.32 units of catechol 2,3-dioxygenase and 0.06, 0.05, 0.05 and 0.03 units of catechol 1,2-dioxygenase, respectively. Cells grown on glucose or succinate had neither activity. Benzoate and all isomers of cresol, creosote, hydroxybenzoates, catechol and methyl catechol were utilized by strain CP4. No chloroaromatic was degraded, either as sole substrate or as co-substrate.The authors are with the Department of Microbiology and Bioengineering, Central Food Technological Research Institute, Mysore-570 013, India     

Biodegradation of polycyclic aromatic hydrocarbons by an acidophilic Stenotrophomonas maltophilia strain AJH1 isolated from a mineral mining site in Saudi Arabia

The present study aims at analyzing the degradation of polycyclic aromatic hydrocarbons (PAHs) at acidic conditions (pH = 2) by acidophilic Stenotrophomonas maltophilia strain AJH1 (KU664513). The strain AJH1 was obtained from an enrichment culture obtained from soil samples of mining area in the presence of PAH as sole sources of carbon and energy. Strain AJH1was able to degrade low (anthracene, phenanthrene, naphthalene, fluorene) and high (pyrene, benzo(e)pyrene and benzo(k)fluoranthene) molecular weight PAHs in acidophilic mineral salt medium at pH 2, with removal rates of up to 95% (LMW PAH) and 80% (HMW PAH), respectively. In addition, strain AJH1 treated petroleum wastewater with 89 ± 1.1% COD removal under acidic condition (pH 2) in a continuously stirred reactor. Acidophilic S. maltophilia strain AJH1, hence holds the promise as an effective degrader for biological treatment of PAHs contaminated wastewater at acidic pH.