INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 7, 2011 © Copyright 2010 All rights reserved Integrated Publishing Association Research article ISSN 0976 – 4402 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview Kumar Arun 1 , Munjal Ashok 1 , Sawhney Rajesh 2 1­ Department of Bioscience and Biotechnology, Banasthali Vidyapith, Banasthali, Rajasthan (India)­304022 2­ Department of Microbiology, Bhojia Institute of Life Sciences, Budh, Baddi. Distt. Solan,Himachal Pradesh (India)­173205 [email protected] ABSTRACT Crude oil, a dark sticky liquid, is a complex mixture of varying molecular weight which is used for the preparation of petroleum products. Crude oil contains more than 30 parent polyaromatic hydrocarbons (PAHs). The U.S.EPA has designated 16 PAH compounds (naphthalene, acenaphthylene, acenaphthene, fluorene, phenenthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a, h]anthracene, benzo[g, h, i]perylene, and indeno[1,2,3­cd]pyrene) as priority pollutants. PAHs are one of the most widespread organic pollutants and potentially health hazard. Besides other environmental components, they are also found in foods (cereals, oils, fats, vegetables, cooked meat). They are carcinogenic , mutagenic , and teratogenic . Thus, key focus is to eliminate these hazardous pollutants from the environment. The present review highlights the presence of various PAHs in the crude oil, key metabolic pathway for the degradation and the associated microbial degraders. The current approach to bioremediation uses various bacterial and fungal genera under aerobic or anaerobic conditions to directly target the specific PAH. However, there is need to explore newer approaches to design an efficient, effective and ecofriendly bioremediation tool. The dearomatization of crude oil might be a useful comprehensive approach and one shot solution to multiple PAH population. Keywords: Crude oil, PAHs, Bioremediation, Phytoremediation, Rhizoremediation 1 Introduction Crude oil is a complex mixture of varying molecular weight hydrocarbons and other organic compounds found beneath the earth's surface. It is a dark sticky fluid naturally­occurring in certain rock formations. Crude oil contains carbon and hydrogen, with or without non­ metallic elements such as oxygen and sulfur. It is highly flammable and generates energy. Its derivative i.e. natural gas, is an excellent fuel. The term "Petroleum" has been used as a synonym to crude oil. This term was first used in the treatise “De Natura Fossilium” published in 1546 by the German mineralogist Georg Bauer (Bauer­Georg et al., 1955). 1.1 Origin, constitution and use Crude oil is the product of heating of ancient organic materials over geological period. It is formed from pyrolysis of hydrocarbon, in a variety of reactions, mostly endothermic at high
Received on March, 2011 Published on April 2011 1420 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview temperature and/or pressure. Crude oil reserves were formed from the preserved remains of prehistoric zooplankton and algae , which had settled to a sea or lake bottom in large quantities under anoxic conditions. On the other hand, the remains of prehistoric terrestrial plants led to form coal. During the formation of crude oil, diagenesis followed catagenesis. The studies documented that over a period, the organic matter mixed with the mud and got buried under heavy layers of sediments resulting in generation of high levels of heat and pressure (diagenesis). This process transformed the organic matter into a waxy material known as kerogen, followed by its further conversion to liquid and gaseous hydrocarbons ( catagenesis). The change from kerogen to natural gas through oil is a temperature dependent event. Sometimes the oil formed at extreme depths migrates and is entrapped at shallower depths. eg. Athabasca oil sands. The crude oil is a heterogeneous entity, composed of hydrocarbon chains of varied lengths. It contains hundreds of different hydrocarbon compounds such as paraffins , naphthenes , aromatics as well as organic sulfur compounds , organic nitrogen compounds and oxygen containing hydrocarbons (phenols). Crude oils generally lack in olefins (Gary et al., 1984). The most common distillations of petroleum are fuels. Fuels generally include, ethane and other short­chain alkanes , diesel fuel (petrodiesel), fuel oils , gasoline (petrol), jet fuel , kerosene, liquefied petroleum gas (LPG). The following table­1 depicts various fuels with their use. Table 1: Different distillations of Petroleum (Fuels) and their use. S. No. 1 2 3 4 5 Fuel/ Derivatives Alkenes (Olefins) Lubricants Uses Manufacture of plastics or other compounds Synthesis of light machine oils, motor oils and greases, as viscosity stabilizers Wax Used in the packaging of frozen foods Petroleum coke Used in carbon products or as solid fuel, Paraffin (asphalt) wax , Aromatic petrochemicals as precursors in other chemical synthesis. Paraffin wax & aromatic As precursor in chemical production petrochemicals The different fractions of the crude oil, produced exhibit boiling point ranges, instead of a single boiling point eg. a crude oil fractionator produces an overhead fraction called "naphtha ". This fraction becomes a gasoline component after it is further processed through a catalytic hydrodesulfurizer and a catalytic reformer into molecules having higher octane rating value (Nelson, 1958; and Gary et al., 1984). 1.2 Variety of PAHs in crude oil PAHs, commonly termed as poly­aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are chemical compounds that consist of fused aromatic rings and do not contain heteroatoms or carry substituents (Fetzer, 2000). The natural crude oil contains significant amounts of polycyclic aromatic hydrocarbons (PAHs) that arise from chemical conversion of natural product molecules, like steroids, to aromatic hydrocarbons. PAHs are
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1421 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview also found in processed fossil fuels, tar and various edible oils (Glenn, 1995). It is described that the distributions of PAHs with respect to the relative amounts of individual PAHs and that of the isomers produced, determine the type of combustion and acts as the indicators of the burning history. The simplest PAHs are phenanthrene and anthracene (International Union on Pure and Applied Chemistry (IUPAC). Benzene and naphthalene have been formally excluded from the list of PAHs. However, they are chemically related to PAHs and referred to as monoaromatic or diaromatics. The literature documents that the number of aromatic rings determine the type of PAHs. The number in PAH may vary from 4 to 7, with 5 or 6 ringed PAH being more common. PAHs composed only of six­membered rings are called alternant PAHs. Certain alternant PAHs, lacking in complete benzene ring, are called "benzenoid" PAHs. The figure­1 and table­2 enlists different PAHs constituents of crude oil. PAHs are classified as small and large depending on the presence of number of rings. The “small” PAHs contain up to six fused aromatic rings where as “large” PAHs contain more than six aromatic rings. PAHs have characteristic UV absorbance spectra with many bands each unique for each ring structure. Thus, each isomer has a different UV absorbance spectrum (200nm­400nm). This helps in the identification of PAHs. Most of the PAHs are also fluorescent. The extended pi­ electron electronic structures of PAHs lead to these spectra, as well as to certain large PAHs also exhibiting semi­conducting and other behaviors. Polycyclic aromatic hydrocarbons are lipophilic . The larger compounds are less water­ soluble and less volatile . These properties gives PAHs, it’s a place in the environment, primarily in soil , sediment and oily substances. However, they are also a component of concern in particulate matter suspended in air. PAHs, the aromatic compounds, exhibit varying degree of aromaticity for each ring segment. Clar's rule, given by Erich Clar in 1964 explains that benzene­like moieties are the most important for the characterization of the properties of PAHs (Kim et al., 2003). The degree of aromacity determines its level of reactivity.
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1422 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview Ova Pen
Ind Nap Pya Azu Hec Hep Hep Bip Trp aIn Cor sIn Rub Ach Hex Hep Flu Tpl Phe Pec Phr Ant Pen Per Flt Acp Per Aca Pic Tpl Ple Npc Chr Pyr Figure 1: Radial depiction showing parent polyaromatic hydrocarbons present in crude oil. Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1423 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview Table 2: Parent Polyaromatic hydrocarbons present in crude oil. S.N. 1. Radial PAH Name Depiction for PAH Pen Pentalene PAH structure Molecular formula 2. Ind Indene C9H8 3. Nap Naphthalene C10H8 4. Azu Azulene C10H8 5. Hep Heptalene C12H10 6. Bip Biphenylene C12H8 7. aIn as­Indacene C12H8 8. sIn s­Indacene C12H8 9. Can Acenaphthylene C12H8 10. Flu Fluorene C13H10 11. Phe Phenalene C13H10 12. Phr Phenanthrene C14H10 13. Ant Anthracene C14H10 14. Flt Fluoranthene C16H10 15. Acp Acephenanthrylene C16H10 16. Aca Aceanthrylene C16H10 17. Tpl Triphenylene C18H12 18. Pyr Pyrene C16H10
C8H6 Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1424 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview 19. Chr Chrysene C18H12 20. Npc Naphthacene C18H12 21. Ple Pleiadene C18H12 22. Per Perylene C20H12 23. Pic Picene C22H14 24. Pen Pentaphene C22H14 25. Pec Pentacene C22H14 26. Tpl Tetraphenylene C24H16 27. Hep Hexaphene C26H16 28. Hex Hexacene C26H16 29. Rub Rubicene C26H14 30. Cor Coronene C24H12 31. Trp Trinaphthylene C30H18 32. Hep Heptaphene C30H18 33. Hec Heptacene C30H18 34. Pya Pyranthrene C30H16 35. Ova Ovalene C32H14 The United States Environmental Protection Agency (USEPA) has designated 16 PAHs compounds as priority pollutants (Table­3). They are naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a, h]anthracene, benzo[g, h, i]perylene, and indeno[1,2,3­cd]pyrene. These priority PAHs are generally targeted for measurement in environmental samples.
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1425 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview Table 3: The U.S. EPA has designated 16 PAH compounds. Naphthalene Phenanthrene Acenaphthylene Acenaphthene Anthracene Benz[a,h] anthracene Chrysene Benz[a] anthracene Pyrene Benzo[a]pyrene Fluorene Fluoranthene Indeno[1,2,3­cd] pyrene Benzo[k] fluoranthene Benzo[g, perylene h, i] Benzo[b] fluoranthene 2. PAHs and Human health PAHs are one of the most widespread organic pollutants and potentially health hazard. In addition to their presence in fossil fuels they are also formed by incomplete combustion of carbon­containing fuels such as wood, coal, diesel, fat, tobacco, or incense. They have been identified as carcinogenic, mutagenic, and teratogenic. PAHs are also found in foods. Studies have shown that most food intake of PAHs comes from cereals, oils and fats. Smaller intakes come from vegetables and cooked meats (Larsson et al., 1983; and Agency for toxic substances and disease registry 1996, European Commission, 2002). The toxicity of PAHs is dependent on its structure and the isomers may exhibit variable toxicity. Benzo[a]pyrene, is the first chemical carcinogen to be discovered. It is one of the constituent found in cigarette smoke . The EPA has classified seven PAH compounds as probable human carcinogens: benz[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, dibenz[a,h]anthracene, and indeno[1,2,3­cd]pyrene. Besides these, Benzo[j]fluoranthene, benzo[ghi] perylene , coronene , and ovalene are known for carcinogenic , mutagenic and teratogenic properties (Luch, 2005).
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1426 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview 3. Bioremoval strategies for PAHs Microorganisms degrade PAHs either via metabolism or co­metabolism. Co­metabolism is especially relevant for the degradation of mixtures of PAHs. Both aerobic and anaerobic metabolism exist for PAH degradation. However aerobic pathways, their kinetics and enzymatic and genetic regulation is well documented. The present focus is on aerobic metabolism of PAHs The metabolic pathways, the degradation kinetics and the enzymatic and genetic regulation are well understood (Wirtz et al., 1981; Digiovanni, 1992; Goyal and Zylstra, 1997). The literature cites four types of aromatic metabolism (Fuchs, 2008): a) Aerobic Metabolism b) Hybrid type aerobic metabolism c) Reductive aromatic metabolism d) Reductive metabolism in anaerobes The flow chart exhibits the aerobic metabolic pathway of degradation for anthracene, as a model compound (Fig 2). The aerobic aromatic metabolism is characterized by the extensive use of molecular oxygen as co­substrate for oxygenases that introduce hydroxyl groups and cleave the aromatic ring. The aerobic PAH catabolism is mediated by the enzymatic activity of dioxygenase/monooxygenase. It incorporates atoms of molecular oxygen into the aromatic nucleus and as a result aromatic ring is oxidized (Digiovanni, 1992; Auger et al., 1995; Goyal et al., 1997,). On the basis of the substituents on the original molecule, two hydroxyl groups may be positioned either ortho (catechol and protocatechuate) or para to each other (gentisate and homogentisate). The cis­dihydrodiols that are formed in this reaction are further oxidized to the aromatic dihydroxy compounds (catechols). These compounds are further oxidized through the ortho or meta cleavage pathways (Denome et al., 1993; Baboshin et al 2008). Finally, the reactions culminate into synthesis of the precursors of TCA cycle (tricarboxylic acid) intermediates. The degradation of all PAHs is carried out by this common scheme. However, its known that the number of aromatic rings govern the kinetic efficiency of the pathway and the type of reaction intermediates produced. Hybrid type aerobic metabolism is used by facultative aerobes eg. aerobic metabolism of benzoate, phenylacetate, and anthranilate. This pathways uses coenzyme A thioesters of the substrates and do not require oxygen for ring cleavage. An oxygenase/reductase leads to dearomatization of the ring.
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1427 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview Anthracene Naphthalene 1, 2­dioxygenase Cis­1, 2­Dihydroanthracene­1, 2­diol Cis­1, 2­dihydrodihydroxy­naphthalene dehydrogenase Anthracene­1, 2­diol Anthracene­1,2­diol­1,2­ dioxygenase Anthracene­1, 2­diol­ 1, 2­dioxygenase 3­[(Z)­2­carboxyvinyl]­2­naphthoate 4­(2­hydroxynaph­3­yl)­2­oxobut­3­enoate 4­(2­hydroxynaph­3­yl)­2­oxobut­3­enoate hydratase­aldolase 6, 7­Benzocoumarin 3­Hydroxy­2­naphthoate 3­hydroxy­2­naphthoate hydroxylase 2, 3­Dihydroxy­naphthalene Phthalate Figure 2: Aerobic oxidation of polyaromatic hydrocarbon (model compound anthracene). In the presence of oxygen, facultative aerobes and phototrophs use a reductive aromatic metabolism. The reduction of the aromatic ring of benzoyl­coenzyme A is catalyzed by
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1428 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview benzoyl­coenzyme A reductase. This reduction is led by the hydrolysis of 2 ATP molecules. It has been documented that a little characterized benzoyl­coenzyme A reductase operates in strict anaerobe as they can not afford the costly ATP­dependent ring reduction (Georg, 2008). Both fungi and bacteria are involved in biodegradation of PAHs (Table 4 & 5). Table 4: Bacterial genera involved in PAHs degradation Bacterial species strain Achromobacter sp. NCW Alcaligenes denitrificans Arthrobacter sp. F101 Arthrobacter sp. P1­1 PAHs References Guo et al., 2008 Weissenfels et al., 1990 Casellas et al., 1997 Carbazole, Seo et al., 2006 Carbazole Fluoranthene Fluorene Phenanthrene, Dibenzothiophene Phenanthrene Phenanthrene Pyrene Arthrobacter sulphureus RKJ4 Acidovorax delafieldii P4­1 Bacillus cereus P21 Bacillus subtilis BMT4i Benzo[a]pyrene (MTCC9447) Phenanthrene Brevibacterium sp.HL4 Burkholderia sp.S3702, RP007, Phenanthrene 2A­12TNFYE­5, BS3770 Burkholderia sp. C3 Burkholderia cepacia BU­3 Samanta et al., 1999 Samanta et al., 1999 Kazunga et al., 2000 Lily et al., 2009 Samanta et al., 1999 Kang et al., 2003, Balashova et al., 1999, Laurie et al., 1999 Seo et al., 2006 Kim et al., 2003 Phenanthrene Phenanthrene Pyrene, Naphthalene xenovorans Benzoate, Biphenyl Burkholderia LB400 Chryseobacterium sp. NCY Cycloclasticus sp. P1 Geobacillus sp. Carbazole Pyrene Napthalene, Fluorene Geobacillus stearothermophilus Anthracene “AAP7919” Janibacter sp. YY­1 Marinobacter NCE312 Mycobacterium sp.PYR, Guo et al., 2008 Wang et al., 2008 Phenanthrene, Bubians et al., 2007 Kumar et al., 2011 Phenanthrene, Fluorene, Yamazoe et al., 2004 Anthracene, Dibenzofuran, Dibenzo­p­dioxin, Dibenzothiophene Naphthalene Hedlund et al., 2001 Benzo[a]pyrene Cheung et al., 2001, Fluoranthene Mycobacterium sp. JS14 Mycobacterium sp. 6PY1, KR2, Pyrene AP1 Mycobacterium sp. RJGII­135 Denef et al., 2005 Benzo[a]pyrene, Grosser et al., 1991 Lee et al., 2007 Rehmann et al., 1998, Vila et al., 2001, Krivobok et al., 2003 Schneider et al., 1996
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1429 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview Benz[a]anthracene Pyrene Mycobacterium LB501T sp.PYR­1, Pyrene, Phenanthrene, Mody et al., 2001, Fluoranthene, Anthracene Kelley et al., 1993, Sepic et al., 1998, Ramirez et al., 2001, Van et al., 2003 Mycobacterium sp. CH1, BG1, Pyrene, Phenanthrene, Fluorene BB1, KR20 Mycobacterium flavescens Mycobacterium PYR­1 Pyrene, Fluoranthene vanbaalenii Phenanthrene Pyrene, Dimethylbenz[a]anthracene Mycobacterium sp. KMS Pyrene Nocardioides aromaticivorans Carbazole IC177 Fluoranthene Pasteurella sp. IFA Naphthalene Polaromonas naphthalenivorans CJ2 Pseudomonas sp. C18, PP2, Phenanthrene, Naphthalene DLC­P11 3­hydroxy­2­ formylbenzothiophene Dibenzofuran Pseudomonas sp. HH69 Chlorinated dibenzo­p­dioxin, Pseudomonas sp. CA10 Carbazole Dibenzofuran, Pseudomonas sp. NCIB 9816­4 Fluorene, Dibenzothiophene Fluorene Pseudomonas sp. F274 Phenanthrene Pseudomonas paucimobilis Pseudomonas vesicularis Fluorene Pseudomonas sp. BT1d Boldrin et al., 1993, Rehmann et al., 2001 Dean­Ross et al., 2002, Dean­Ross et al., 1996 Kim et al., 2005, Moody et al., 2003 Miller et al., 2004 Inoue et al., 2006 Sepic 1999 Pumphrey et al., 2007 Denome et al., 1993, Prabhu et al., 2003 Bressler et al., 2001 Fortnagel et al., 1990 Habe et al., 2001 Resnick et al., 1996 Grifoll et al., 1994 Weissenfels et al., 1990 Weissenfels et al., 1990 OUS82 Pseudomonas putida P16, BS3701, BS3750, BS590­P, BS202­P1 Phenanthrene, Naphthalene Pseudomonas fluorescens BS3760 Phenanthrene, Benz[a]anthracene, Balashova et al., 1999 Chrysene Pseudomonas stutzeri P15 Pyrene Kiyohara et al., 1994, Balashova et al., 1999 Kazunga et al., 2000
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1430 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview Pseudomonas saccharophilia Pseudomonas aeruginosa Ralstonia sp. SBUG 290, U2 Pyrene Rhodanobacter sp. BPC­1 Rhodococcus sp. Benzo[a]pyrene Pyrene, Fluoranthene Rhodococcus sp. WU­K2R Benzothiophene, Naphthothiophene Alkylated dibenzothiophene Dibenzothiophene Phenanthrene Benzo[a]pyrene Rhodococcus erythropolis I­19 Rhodococcus erythropolis D­1 Staphylococcus sp. PN/Y Stenotrophomonas maltophilia VUN 10,010 Stenotrophomonas maltophilia VUN 10,003 Sphingomonas yanoikuyae R1 Sphingomonas yanoikuyae JAR02 Phenanthrene Naphthalene, Dibenzofuran Kazunga et al., 2000 Romero et al., 1998 Becher et al., 2000, Zhou et al., 2002 Kanaly et al., 2002 Dean­Ross et al., 2002, Walter et al., 1991 Kirimura et al., 2002 Folsom et al., 1999 Matsubara et al., 2001 Mallick et al., 2007 Boonchan et al., 1998 Pyrene, Fluoranthene Pyrene, Fluoranthene, Juhasz et al., 2000 Benz[a]anthracene Pyrene Kazunga et al., 2000 Benzo[a]pyrene Rentz et al., 2008 Sphingomonas sp.P2, LB126 Phenanthrene, Fluoranthene, Pinyakong et al., 2003, Fluorene, Anthracene Van et al., 2003, Sphingomonas sp. Dibenzofuran, Carbazole, Gai et al., 2007 Dibenzothiophene Phenanthrene, Fluoranthene, Story et al., 2001, Anthracene, Naphthalene Pinyakong et al., 2000 Sphingomonas paucimobilis EPA505 Sphingomonas wittichii RW1 Sphingomonas sp. KS14 Terrabacter sp.DBF63 Chlorinated dibenzo­p­dioxin Phenanthrene, Naphthalene Fluorene, Dibenzofuran, Chlorinated dibenzo­p­dioxin, Chlorinated dibenzothophene Xanthamonas sp. Benzo[a]pyrene Mueller et al., 1990 Nam et al., 2006 Cho et al., 2001 Habe et al., 2004, Habe et al., 2001, Habe et al., 2002 Grosser et al., 1991 Pyrene, Carbazole White rot fungi often prepare aromatic compounds for ring cleavage by first converting them to quinones. The initial oxidation of anthracene (to 9,10­anthraquinone), benzo[a]pyrene ( Haemmerli, et al., 1986 ) and several other PAHs is catalyzed by lignin peroxidases from Phanerochaete chrysporium, Bjerkandera sp. strain BOS55 (Field, J.A. et al., Enzyme and Micro. Tech. 18:300­308, 1996) and other white rot fungi. Manganese peroxidases, another family of lignin degrading peroxidases produced by white rot fungi, can also oxidize anthracene (Eibes et al., 1986). Laccases, copper­containing enzymes that are also involved in lignin degradation by Trametes versicolor, have also been shown to oxidize anthracene ( Collins et al., 1986 ). Not all white rot fungi produce laccases. P. chrysosporium can completely mineralize anthracene. It cleaves 9,10­anthraquinone to phthalate and, here
Kumar Arun, Munjal Ashok, Sawhney Rajesh International Journal of Environmental Sciences Volume 1 No.7, 2011 1431 Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: an overview proposed, catechol, though o­benzoquinone or aliphatic compounds are also possible ( Hammel et al., 1991). Table 5: Fungal genera capable of degrading PAHs. Name of Fungus Phanerochaete chrysporium Bjerkandera sp. strain BOS55 Trametes versicolor Cunninghamella elegansoxidizes P. chrysosporium Aspergillus flavus Paecilomyces farinosus PAH Anthracene Anthracene Reference Field et al.,1996 Field, et al.,1996 Anthracene Anthracene Collins et al., 1986 Cernigilia, 1997 Anthracene Benzo[a]pyrene Benzo[a]pyrene Hammel et al., 1991 Romero et al., 2010 Romero et al., 2010 Different technologies such as biostimulation, bioaugmentation, bioaccumulation, biosorption, phytoremediation and rhizoremediation are the key focus of present bioremediation strategies. 4. Conclusion Crude oil contains variety of PAHs, which are known pollutants and potential health hazards. Besides other approaches, dearomatization of crude oil might be a direct hit to target and curb the PAH pollution. Voluminous researches have evolved different bioremediation tools in the form of efficient bacteria and fungi as potential degraders. The metabolism involved in degradation pathways is also well understood. The present day developments and newer approaches primarily focus to target the specific PAHs. However, development of precise, effective and composite technology to treat the complex mixtures is still a matter of concern. Acknowledgement We are thankful to Professor Aditya Shastri for kindly extending “Banasthali Centre for Education and Research in Basic Science” sanctioned under CURIE (Consolidation of University Research for Innovation and Excellence in Women University) program of department gratefully acknowledged. The authors are indebted to Bhojia Charitable Trust for Science Research and Social Welfare for providing adequate facilities to prepare this manuscript. 5. References 1. Auger, R.L., Jacobson, A.M., Domach, M.M. 1995. Effect of nonionic surfactant addition on bacterial metabolism of naphthalene: Assessment of toxicity and overflow metabolism potential. Journal of Hazardous Materials. 43: pp 263­272. 2. Bauer Georg, B., Bandy Mark Chance (tr.), Bandy Jean A.(tr.) . 1955. De Natura Fossilium. Translated.
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