Biodegradation overview

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  • 1.BIODEGRADATION- OVERVIEW & BIODEGRADATION OFHYDROCARBONS & PCBGunjan Mehta Deptt. of Biotechnology,Virani Science College, Rajkot

2. Degradation Degradation is breakdown of complex organicmaterial into simpler one. Different ways of degradation: 1. Photodegradation by natural day light 2. Oxidation by chemical additives(Catalysts) 3. Thermal degradation by heat 4. Mechanical degradation by mechanical force 5. Biodegradation by Microorganisms. 3. Degradation Three levels of degradations: 1. Rapid degradation(day- week): HC compounds 2. Slow breakdown(Months- years): HC polymers/Halogenated compounds 3. No degradation: Recalcitrant/ Xenobiotic: Plastic 4. Biodegradation Naturalandcomplex process ofdecomposition facilitated by biochemicalreactions. It is biological transformation of an complex organicmaterial to simpler by Mos. Reduced organic materials are thermodynamicallyunstable and oftenly attacked by microbialenzymes. Biodegradibility: Quality, representing thesusceptibility of the substrate to biologicaltransformation. 5. Types of Biodegradation1. Primary biodegradation: Biochemical ways of catalystswheretransformation or alteration in chemical structure ofa compound occurs by biochemical reactions. Results in loss of specific property- partialbiodegradation and leaves molecule mostly intact. Not desirable due to toxicity issues. Ex. Change in toxic halogen gp from Pera to Metaposition. Azo dye Amino benzene 6. Types of Biodegradation2. Acceptable biodegradation: Biological conversion of toxic compounds to nontoxic by biological means. Removal of undesirable characteristics occurs. Complete removal of toxic entity occurs. 7. Types of Biodegradation3. Ultimate biodegradation: The level of degradation where the compound istotally utilized and results in production of CO2 andwater and mineral constituents. Molecular cleavage is so extensive that it removesall chemical, biological and toxic properties. The ultimate products are highly stable and cantbe degraded further. Ex. 8. Reactions involved inBiodegradation Oxidative reaction Reductive reaction Hydrolytic reaction (water) Conjugative reaction (Methylation, Acetylation) 9. Factors affecting BiodegradationEnvironmSubstrate Organis ent relatedm related related 10. Factors affecting Biodegradation Nature of pollutants Physiochemical properties Substrate ConcentrationrelatedBiodegradabilityToxicityChemical natureVolatilityPolarity 11. Factors affecting Biodegradation Population density Organism CompositionrelatedIntra/ Inter specific interaction Enzyme activityTurn over numberAdaptation 12. Factors affecting BiodegradationTemperature Environment pH related Oxygen availability Nutrient sources- C & e- Salinity 13. Organisms responsible forbiodegradationMost significant group of living organism involved inbiodegradation, responsible for 65% total metabolismdue higher growth rate and biomass.Higher organism are also involved but notsignificantly, inability to degrade complex molecule.Microbes represent most diversified metabolism onearth.Microbes--------Complex material-----simpler formMicrobes utilize energy more efficiently in comparison tohigher organisms.High rate of reproduction and mutation is the governingfactor. 14. Organisms responsible forbiodegradation Other lower organism- algae and invertebrates toopossess some of the criteria- Earthworm, but theirbiodegradative potential is still unknown. Marine biodegraders: Bacteria and Fungi Soil biodegraders: Bacteria and Fungi Mutations are very often in bacteria and is veryuseful for progressive adaptation towards thebiodegradation pathways. Not all microbe are equipped with all enzyme, somany of them follow.COMETABOLISM 15. Organisms responsible forbiodegradation 16. BiodegradationThree categories of biodegradation:I. Usable immediately II. Usable followingacclimatization III. Recalcitrant IV. 17. Reactions involved inBiodegradation I. Usable immediately Simple sugars, amino acids and fatty acids- directutilization. The enzymes required for breakdown are eitherconstitutive or inducible. This requires minimum acclimatization period. II. Usable following the acclimatization: A lag phase is required for adaptation where nodegradation or very little degradation occurs. 18. Reactions involved inBiodegradation During lag phase induction of enzyme occurs Duration of acclimatization period varies from fewhrs to days or even weeks depending onbiodegradability. Example: lag phase of 50 days inpyrazondegradation. III. Recalcitrant/ Xenobiotic: Naturally occurring substances such as lignin aswell as antropogenic. 19. Degradation of petroleum hydrocarbon Aliphatic hydrocarbon belongs to mainly threegroups: Aliphatic Hydrocarbon Alkane AlkeneAlkyne 20. Alkane biodegradation Aliphatic hydrocarbons are more saturatedcompared to aromatic.Saturation Biodegradation Branching of the aliphatic chain reduces the rate ofbiodegradation. Alkanes are most commonly metabolized byterminal methyl oxidation. Monooxygenase enzyme plays a key role in that. O2 MonooxygenaseO atom added to 1 or 2 alkane and other atom is reduced to H2O 21. Alkane biodegradation Reduced NADP that is NADPH2 serve as e-donorand oxidizes alkane aldehyde Fatty acid -oxidation CO2+ H2O Sometimes both terminal methyl groups are oxidizedresults in formation of dicarboxylic acid. 22. Alkane biodegradation 23. Branched Alkane biodegradation 24. Alkene biodegradation CH3- (CH2)n- CH= CH2HOOC- (CH2)n-CH= CH2 CH3- (CH2)n- CH2O= CH2OSat. end oxidationFormation of diol Further oxidation to Carboxylic acid - oxidation 25. Degradation of alicyclichydrocarbon Waxes, Plant Oils, microbial lipids, Cyclohexane. Hydroxylation of alicyclic alcohol byMonooxigenase enzyme catalyzed reaction anddehydrogenation by dehydrogenase enzyme leadsto formation of ketone. Further oxidation inserts oxygen into ring andlectone is formed. Ring cleavageLinearizedAldehydeCarboxylicacid 26. Biodegradation of aromatichydrocarbonsMost notorious environmental pollutants due to stability.Example: Polychlorinated Biphenyls (PCBs) Polyaromatic hydrocarbons(PAHs) The principle reason behind increased resistanceto biodegradation is.. Introductionof electronegative groups such asChloride, Sulfate, Nitrate. Lowered reactivity of aromatic HC due to halogenconjugate which decreases interaction with O2 27. Biodegradation of aromatichydrocarbons They are oxidized by dioxygenase enzyme whichincorporates 2 oxygen atoms leading to formationof CATECHOL. Dihydroxylated aromatic HC- CATECHOL iscleaved by two ways1. Orthocleavage Ring cleavage between twoadjacent hydroxyl group by 1,2- Dioxygenase2. Metacleavage Ring cleavage between thecarbon atom containing hydroxyl group and adjacentcarbon without hydroxyl group by 2,3- Dioxygenase 28. Example: Benzene biodegradation Conversion of benzene to Catechol: 29. Orthocleavage: Benzenebiodegradation 30. Metacleavage: Benzenebiodegradation 31. Crude Oil biodegradation Crude oil= aliphatic HC+ alicyclic HC+ aromatic HC Auto- oxidation in absence of light plays minor rolebecause low temperature of marine environment provideno opportunity for activation. However, photo- oxidation contribute significantly for selfpurification of marine environment. Lab. experiments suggests that, 8 Hrs of effectivephotoemission may destroy 0.2 metric tons of oil persquare Km. 32. Crude Oil biodegradation More than 100 spp of bacteria, yeast and fungi arecapable of oxidizing crude oil. For ex. Pseudomonas spp, Methanomonasspp, Nocardia spp Since oil is deficient in some microbialnutrients(especially N, P), so nitrate & phosphate areadded to accelerate mineralization. Optimum temperature: 20- 35C Free/ Dissolved oxygen Turbulent condition 33. Biodegradation of halogenated HCCarbon halogen bond- highly stable and cleavage of this bond requires substantial energy input.It is an endothermic reaction.In aliphatic halogenated compound, complete degradation occurs in two stages-1. Removal of halogen2. Degradation of organic entityRemoval of halogen occurs by two possible mechanisms. 34. Biodegradation of Halogenated HC 1. Elimination of hydrogen halide: Direct removal of hydrogen halide between twoadjacent carbon atom yields double bond and suchreaction occurs rarely. 35. Biodegradation of Halogenated HC2. Substitution of halogen group by(a) H group (Reductive reaction)(a) -OH group 36. Biodegradation of Halogenated HC S (thio) group: Most common type of reaction is OH, whichincorporate reactive oxygen group into it. 37. Biodegradation of Halogenated HCElimination of halide occurs by two possible routes:(a) Elimination of halide after ring cleavage(b) Elimination of halide before ring cleavage(A) Elimination of halide after ring cleavage:Aerobic degradation of chlorinated aromatic compoundusually achieved by a sequence of reaction.HydroxylationCleavage- aromatic ringElimination of cl- from aliphatic intermediate. 38. Biodegradation of Halogenated HC The pathway 1. Formation of cl- catechol: The key intermediate in degradation of many chlorinated compounds. 39. Biodegradation of Halogenated HC The pathway 2. Oxidation by Orthocleavage & Metacleavage: Orthocleavage leads to ring cleavage by 1,2dioxygenase enzyme followed by elimination ofhalogen entity. The remaining non halogenatedproduct can be metabolized further. Metacleavage produces highly toxic intermediateand cant be taken further by organism involved inbiodegradation. 40. Ortho cleavage 41. Meta cleavage 42. Biodegradation of Halogenated HC The pathway(B) Elimination of halide before ring cleavage:This is not a common pathway. 1. Formation of chlorocatechol: 43. Biodegradation of Halogenated HC The pathway2. Further oxidation by ortho & Meta cleavage:Ortho cleavage: 44. Biodegradation of Halogenated HC The pathway Meta cleavage: