BIODEGRADATION AND METABOLISM OF PETROCHEMICAL

1. SHAHEEN ALAM
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BIODEGRADATION AND METABOLISM OF PETROCHEMICAL
One of the majorenvironmental problemstodayishydrocarboncontaminationresultingfromthe
activitiesrelatedtothe petrochemicalindustry.Hydrocarboncomponentshave beenknowntobelong
to the familyof carcinogensandneurotoxicorganicpollutants.
Componenetsofpetroleumhydrocarbon: Petroleumisacomplex mixtureof
i. Aliphatichydrocarbons,
ii. Alicyclic(cycloaliphaticsaturatedringstructures) hydrocarbons
iii. Aromatichydrocarbons
iv. A smallerproportionof non-hydrocarboncompounds suchas –naphthenicacids,phenols,
thiols,heterocyclicnitrogenandsulfurcompounds,aswell asmetalloporphyrins
How spill occure: Leaksand accidental spillsoccurregularlyduringthe exploration,production,refining,
transport,and storage of petroleumandpetroleum products.
Example of successful oil spill biodegradation: The successof bioremediationeffortsinthe cleanupof
the oil tankerExxonValdezoil spillof 1989 inPrince WilliamSoundandthe Gulf of Alaskacreated
tremendousinterestinthe potential of biodegradationandbioremediationtechnology
Harmful effect
 Oil floatingonwateristechnicallydifficulttocontainandcollect,itisdestructive tobirdsand
variousformsof marine life and,whendrivenashore,causesheavyeconomicandesthetic
damage
 In additiontokillingbirds,fish,shellfish,andotherinvertebrates,oil pollutionappearsalsoto
have more subtle effectsonmarine life.Dissolvedaromaticcomponentsof petroleumdisrupt,
evenat a lowppbconcentration,the chemoreceptionof some marine organisms.Asfeeding
and mating responses largelydependonchemoreception.suchdisruptioncanleadto
eliminationof manyspeciesfromthe pollutedareaevenwhenthe pollutantconcentrationisfar
belowthe lethal levelasdefinedinthe conventional sense.
 Anotherdisturbingpossibilityisthatsome condensedpolynuclearcomponentsof petroleum
that are relativelyresistanttobiodegradationandare carcinogenicmaymove upmarine food
chainsand taintfishor shellfish.
Non biological treatment
Currentlyaccepteddisposal methodsof incinerationorburial insecure landfillscanbecome
prohibitivelyexpensive whenamountsof contaminantsare large.Mechanical andchemical methods
such as, dispersingof the oil withthe use of detergentsorsinkingthe oil withchalkor siliconizedsand
are essentiallycosmeticmeasures.Theyremove the oil fromthe surface butincrease the exposure of
marine life tothe pollutantandare,therefore,bestavoided.

2. SHAHEEN ALAM
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Biological treatment
Bioremediationisthe promisingtechnologyforthe treatmentof these contaminatedsitessince itis
cost-effective andwill leadtocomplete mineralization.Bioremediationfunctionsbasicallyon
biodegradation,whichmayrefertocomplete mineralizationof organiccontaminantsinto carbon
dioxide,water,inorganiccompounds,andcell proteinortransformationof complexorganic
contaminantstoothersimplerorganiccompoundsbybiological agentslikemicroorganisms.Many
indigenousmicroorganismsinwaterandsoil are capable of degradinghydrocarboncontaminants.
Factors that influence the rate of PetroleumBiodegradation
Numerousscientificreviewarticleshave coveredvariousfactorsthatinfluence the rate of oil
biodegradation -
1. One importantrequirementisthe presence of microorganismswiththe appropriate metabolic
capabilities
2. Temperature playsanotherimportantrole inbiodegradationof hydrocarbonsbydirectly
affectingthe chemistryof the pollutantsaswell asaffectingthe physiologyanddiversityof the
microbial flora.Some scientistfoundthatatlow temperatures,the viscosityof the oil increased,
while the volatilityof the toxiclow molecularweighthydrocarbonswere reduced,delayingthe
onsetof bio degradation.Temperature alsoaffectsthe solubilityof hydrocarbonsThe rate of
biodegradationgenerallydecreaseswiththe decreasingtemperature somestudiesshow that
highestdegradationratesthatgenerallyoccurinthe range 30–40◦C insoil environments,20–
30◦C in some freshwaterenvironmentsand15–20◦C in marine environments.Significant
biodegradationof hydrocarbonshave beenreportedinpsychrophilicenvironments.
3. Nutrientsare veryimportantingredientsforsuccessfulbiodegradationof hydrocarbon
pollutantsespeciallynitrogen,phosphorus,andinsome casesiron.Some of these nutrients
couldbecome limitingfactorthusaffectingthe biodegradationprocesses.Some scientist
reportedthatwhena majoroil spill occurredinmarine andfreshwaterenvironments,the
supplyof carbon wassignificantlyincreasedand the availabilityof nitrogenandphosphorus
generallybecame the limitingfactorforoil degradation.Inmarine environments,itwasfound
to be more pronounceddue tolow levelsof nitrogenandphosphorousinseawater.Freshwater
wetlandsare typicallyconsideredtobe nutrientdeficientdue toheavydemandsof nutrientsby
the plants.Therefore,additionsof nutrientswerenecessarytoenhance the biodegradationof
oil pollutant.
On the otherhand,excessivenutrientconcentrationscanalsoinhibitthe biodegradationactivity.
Several authorshave reportedthe negative effectsof highNPKlevelsonthe biodegradationof
hydrocarbonsespeciallyonaromatics.
4. Some scientistreported thatphotooxidationincreasedthe biodegradabilityof petroleum
hydrocarbonbyincreasingitsbioavailabilityandthusenhancingmicrobial activities.

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5. The physical andchemical characteristicsof the oil andoil surface area are also important
determinantsof bioremediationsuccess.
Approach: There are the two mainapproachestooil spill bioremediation:
(a) bioaugmentation,inwhichknownoil-degradingbacteriaare addedtosupplementthe existing
microbial population,and
(b) biostimulation,inwhichthe growthof indigenousoil degradersisstimulatedbythe additionof
nutrientsorothergrowth-limitingcosubstrates
Mechanism: Generallythere are twomicrobial metabolismpathwaysforPetroleumhydrocarbon
degradation-
1) Aerobicprocess
2) Anaerobicprocess
 AerobicProcess : The initial attack on alkanes occurs by enzymes that have a strict requirement
for molecular oxygen. that is monooxygenases (mixed function oxida.ses) or dioxygenases
Aerobically,alkanesmaybe attacked monoterminallyatthe terminal methyl group, forminga primary
alcohol that in turn, is further oxidized to an aldehyde and fatty acid. Occasionally, both terminal methyl
groups are oxidized in this manner, resulting in the formation of a dicarboxylic acid.

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Once a fatty acid is formed, further catabolism occurs by the beta-oxidation sequence. The end products
of hydrocarbon mineralization , thus are CO2 and H2O
Aerobicbiodegradartionof Cyclohexane:
In the case of
cyclohexane
hydroxylation by a
monooxygenase leads to
an alicyclic alcohol.
Dehyd rogenation leads
to the keone. Further
oxidation inserts an
oxygen into the ring and
a lactone is formed. The
hydroxyl group is
oxidized, in sequence, to
an aldehyde and carboxyl
group. The resulting
dicarboxylic acid is
further metabolized by
Beta-oxidation.
Figure:Aerobicbiodegradationof Alkane to
Fatty acid to CO2 and H2O

5. SHAHEEN ALAM
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Aerobic biodegradation of Naphthalene :
Condensed aromaticring
structures, if degradable,
are also attacked by
dihydroxylation and the
opening of one of the rings.
The opened ring is
degraded to pyruvic acid
and C02, and a second ring is
attacked in the same
fashion. Many condensed
polynuclear aromatic
compounds, however, are
degraded only with
difficulty or not at all.

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Aerobic biodegradation of Aromatic ring (Benzene):
Aromatic hydrocarbons are oxidized by dioxygenases to labile cis,cis-dihydrodiol that
spontaneously convert to catechols. The dihydroxylated aromatic ring is opened by oxidative
“ortho cleavage,” resulting in cis,cis-muconic acid. This is metabolized further to keto-adipic
acid, which is oxidatively cleaved to the common TCA intermediates, succinic acid, and acetyl-
CoA. Alternatively, the catechol ring may be opened by meta cleavage, adjacent to rather than
between the hydroxyl groups, yielding 2-hydroxycis, cis-muconic semialdehyde. Further
metabolism leads to formic acid, pyruvic acid, and acetaldehyde

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Othermechanismsinvolvedare
(1) attachmentof microbial cells tothe substrates and
(2) productionof biosurfactants[76].
The uptake mechanismlinkedtothe attachmentof cell tooil dropletisstill unknownbutproductionof
biosurfactantshas beenwell studied. Biosurfactantsare heterogeneousgroupof surface active chemical
compoundsproducedbya wide varietyof microorganisms.Surfactantsenhance solubilizationand
removal of contaminants.Biodegradationisalsoenhancedbysurfactantsdue toincreased
bioavailabilityof pollutants. Microbial consortiumconsistingof twoisolatesof Pseudomonas
aeruginosaandone isolate Rhodococcuserythropolisfromsoil contaminatedwithoilysludgewasused
inthisstudy.
 AnaerobicProcess :-
 Anaerobic attack of alkanes and alkenes was believed possible only if these compounds
carried one or more substituents, in particular halogens. Dichloromethane CH2Cl2 can be
degraded anaerobically. In these reactions, the initial attack cannot involve oxygenation
but instead involves dechlorination step. In the case of dichloromethane, the proposed
reaction carried out by a consortium of two different bacterial strains is summarized as
This reaction is followed by an oxidation of the formaldehyde-like intermediate (HCHO) to
formic acid. The formic acid is subsequently converted to acetate in an acetogenic reaction .

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 In the case of tetra- and trichloroethylene,anaerobicdechlorinationbyreductive processhas
beenobserved.Inthe process,the chlorinatedhydrocarbonservesasterminal electron
acceptor .
 The formationof ethane byreductive transformationof tetra-chloroethene.A clear
demonstrationthatasaturated,unsubstitutedalkane canbe mineralizedbyanaerobicsulfate-
reducingbacterium,strainHxD3,fromthe precipitate of anoil–waterseparatorinanoil field
nearHamburg, Germany.Thisorganismmineralizedhexadecane usingsulfateasoxidant
(terminal electronacceptor).
 Anaerobicscissionof the ringstructure involvesringsaturation,hydration,and
dehydrogenation.Somearomatichydrocarbonssuchasbenzoate canalsobe biodegraded
anaerobicallybyphotometabolismof certain Rhodospirillaceae(purple nonsulfurbacteria).Ring
cleavage isbyhydrationof pimelate
 Unlike chorinatedalkanes,chlorinatedaromaticshave beenshowntobe completelydegradable
anaerobically,byaconsortiumof bacteria.Inone kindof consortium, Desulfomoniletiedjei
DCB-1 acts on a chlorinatedhydrocarbonbyusingitas terminal electronacceptorina
respiratoryprocessthatincludesdechlorination.Subsequentmineralizationof the
dechlorinatedaromaticproductdependsonotheranaerobicorganismsinthe consortium.
Othermechanismsinvolvedare
(1) attachmentof microbial cells tothe substrates and
(2) productionof biosurfactants
The uptake mechanismlinkedtothe attachmentof cell tooil dropletisstill unknownbutproductionof
biosurfactantshas beenwell studied. Biosurfactantsare heterogeneousgroupof surface active chemical
compoundsproducedbya wide varietyof microorganisms.Surfactantsenhance solubilizationand
removal of contaminants.Biodegradationisalsoenhancedbysurfactantsdue toincreasedbioavail-
abilityof pollutants. Microbial consortiumconsistingof twoisolatesof Pseudomonasaeruginosa and
one isolate Rhodococcuserythropolis fromsoil contaminatedwithoilysludgewasusedinthisstudy.

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Other Petroleumhydrocarbon degrading organisms :-
BesidesBacterial genera,some fungal genera,namely,Amorphoteca,Neosartorya,Talaromyces,and
Graphium and yeastgenera,namely, Candida,Yarrowia, andPichia were isolatedfrompetroleum
contaminatedsoil andprovedtobe the potential organismsforhydrocarbondegradation.Some
scientistalsoreportedagroupof terrestrial fungi,namely,Aspergillus,Cephalosporium,and Pencillium
whichwere alsofoundtobe the potential degraderof crude oil hydrocarbons.
The yeastspecies,namely, Candida lipolytica, Rhodotorula mucilaginosa, Geotrichumsp,and
Trichosporon mucoides isolatedfromcontaminatedwaterwere notedtodegrade petroleum
compounds.
Algae are alsothe importantmembersforpetrolelumhydrocarbondegradation. .Walkeretal.[51]
isolatedanalga, Prototheca zopfiwhichwas capable of utilizingcrude oil anda mixedhydrocarbon
substrate andexhibitedextensivedegradationof n-alkanesandiso-alkanesaswell asaromatic
hydrocarbons.Cernigliaetal. observedthatnine cyanobacteria,five greenalgae,one redalga,one
brownalga,and two diatomscouldoxidizenaphthalene.
Protozoa, by contrast,had notbeenshowntoutilize hydrocarbons.

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REFERENCE FOR THIS Topics :
1) Microbial Ecology: Fundamentals And Applications, 4/E
By Ronald M. Atlas, Richard Bartha
2) GEOMICROBIOLOGY, Fourth Edition, Revised and Expanded
By Henry Lutz Ehrlich
3) Review Article
Microbial Degradation of Petroleum Hydrocarbon Contaminants: An Overview
https://www.researchgate.net/file.PostFileLoader.html?id=57519fdf217e204c405
965e5&assetKey=AS%3A368913058680833%401464967135767