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Biodegradation overview


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  • 1. BIODEGRADATION- OVERVIEW & BIODEGRADATION OFHYDROCARBONS & PCB Gunjan Mehta Deptt. of Biotechnology, Virani Science College, Rajkot
  • 2. Degradation Degradation is breakdown of complex organic material 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 “Natural and complex process of decomposition facilitated by biochemical reactions.” It is biological transformation of an complex organic material to simpler by Mos. Reduced organic materials are thermodynamically unstable and oftenly attacked by microbial enzymes. Biodegradibility: Quality, representing the susceptibility of the substrate to biological transformation.
  • 5. Types of Biodegradation1. Primary biodegradation: Biochemical ways of catalysts where transformation or alteration in chemical structure of a compound occurs by biochemical reactions. Results in loss of specific property- partial biodegradation and leaves molecule mostly intact. Not desirable due to toxicity issues. Ex. Change in toxic halogen gp from Pera to Meta position. Azo dye Amino benzene
  • 6. Types of Biodegradation2. Acceptable biodegradation: Biological conversion of toxic compounds to non toxic 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 is totally utilized and results in production of CO2 and water and mineral constituents. Molecular cleavage is so extensive that it removes all chemical, biological and toxic properties. The ultimate products are highly stable and can’t be degraded further. Ex.
  • 8. Reactions involved inBiodegradation Oxidative reaction Reductive reaction Hydrolytic reaction (water) Conjugative reaction (Methylation, Acetylation)
  • 9. Factors affecting Biodegradation EnvironmSubstrate Organis ent related m related related
  • 10. Factors affecting Biodegradation Nature of pollutants Physiochemical properties Substrate Concentration related Biodegradability Toxicity Chemical nature Volatility Polarity
  • 11. Factors affecting Biodegradation Population density Organism Composition related Intra/ Inter specific interaction Enzyme activity Turn over number Adaptation
  • 12. Factors affecting Biodegradation Temperature Environment pH related Oxygen availability Nutrient sources- C & e- Salinity
  • 13. Organisms responsible forbiodegradation Most significant group of living organism involved in biodegradation, responsible for 65% total metabolism due higher growth rate and biomass. Higher organism are also involved but not significantly, inability to degrade complex molecule. Microbes represent most diversified metabolism on earth. Microbes--------Complex material-----simpler form Microbes utilize energy more efficiently in comparison to higher organisms. High rate of reproduction and mutation is the governing factor.
  • 14. Organisms responsible forbiodegradation Other lower organism- algae and invertebrates too possess some of the criteria- Earthworm, but their biodegradative potential is still unknown. Marine biodegraders: Bacteria and Fungi Soil biodegraders: Bacteria and Fungi Mutations are very often in bacteria and is very useful for progressive adaptation towards the biodegradation pathways. Not all microbe are equipped with all enzyme, so many of them follow….COMETABOLISM
  • 15. Organisms responsible forbiodegradation
  • 16. Biodegradation Three 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- direct utilization. The enzymes required for breakdown are either constitutive or inducible. This requires minimum acclimatization period. II. Usable following the acclimatization: A lag phase is required for adaptation where no degradation or very little degradation occurs.
  • 18. Reactions involved inBiodegradation During lag phase induction of enzyme occurs Duration of acclimatization period varies from few hrs to days or even weeks depending on biodegradability. Example: lag phase of 50 days in pyrazon degradation. III. Recalcitrant/ Xenobiotic: Naturally occurring substances such as lignin as well as antropogenic.
  • 19. Degradation of petroleum hydrocarbon Aliphatic hydrocarbon belongs to mainly three groups: Aliphatic Hydrocarbon Alkane Alkene Alkyne
  • 20. Alkane biodegradation Aliphatic hydrocarbons are more saturated compared to aromatic. Saturation α Biodegradation Branching of the aliphatic chain reduces the rate of biodegradation. Alkanes are most commonly metabolized by terminal methyl oxidation. Monooxygenase enzyme plays a key role in that. O2 MonooxygenaseO 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-donor and oxidizes alkane aldehyde Fatty acid β- oxidation  CO2+ H2O Sometimes both terminal methyl groups are oxidized results in formation of dicarboxylic acid.
  • 22. Alkane biodegradation
  • 23. Branched Alkane biodegradation
  • 24. Alkene biodegradation CH3- (CH2)n- CH= CH2 HOOC- (CH2)n-CH= CH2 CH3- (CH2)n- CH2O= CH2O Sat. end oxidation Formation of diol Further oxidation to Carboxylic acid β- oxidation
  • 25. Degradation of alicyclichydrocarbon Waxes, Plant Oils, microbial lipids, Cyclohexane. Hydroxylation of alicyclic alcohol by Monooxigenase enzyme catalyzed reaction and dehydrogenation by dehydrogenase enzyme leads to formation of ketone. Further oxidation inserts oxygen into ring and lectone is formed. Ring cleavageLinearizedAldehydeCarboxylic acid
  • 26. Biodegradation of aromatichydrocarbonsMost notorious environmental pollutants due to stability.Example: Polychlorinated Biphenyls (PCBs) Polyaromatic hydrocarbons(PAHs) The principle reason behind increased resistance to biodegradation is…..  Introductionof electronegative groups such as Chloride, Sulfate, Nitrate.  Lowered reactivity of aromatic HC due to halogen conjugate which decreases interaction with O2
  • 27. Biodegradation of aromatichydrocarbons They are oxidized by dioxygenase enzyme which incorporates 2 oxygen atoms leading to formation of CATECHOL. Dihydroxylated aromatic HC- CATECHOL is cleaved by two ways…1. 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 role because low temperature of marine environment provide no opportunity for activation. However, photo- oxidation contribute significantly for self purification of marine environment. Lab. experiments suggests that, 8 Hrs of effective photoemission may destroy 0.2 metric tons of oil per square Km.
  • 32. Crude Oil biodegradation More than 100 spp of bacteria, yeast and fungi are capable of oxidizing crude oil. For ex. Pseudomonas spp, Methanomonas spp, Nocardia spp Since oil is deficient in some microbial nutrients(especially N, P), so nitrate & phosphate are added to accelerate mineralization. Optimum temperature: 20- 35ºC Free/ Dissolved oxygen Turbulent condition
  • 33. Biodegradation of halogenated HC Carbon 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 entity Removal of halogen occurs by two possible mechanisms….
  • 34. Biodegradation of Halogenated HC 1. Elimination of hydrogen halide: Direct removal of hydrogen halide between two adjacent carbon atom yields double bond and such reaction occurs rarely.
  • 35. Biodegradation of Halogenated HC 2. 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, which incorporate reactive oxygen group into it.
  • 37. Biodegradation of Halogenated HC Elimination 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.HydroxylationCleavage- aromatic ringElimination 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 1,2 dioxygenase enzyme followed by elimination of halogen entity. The remaining non halogenated product can be metabolized further. Metacleavage produces highly toxic intermediate and can’t be taken further by organism involved in biodegradation.
  • 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 pathway2. Further oxidation by ortho & Meta cleavage:Ortho cleavage:
  • 44. Biodegradation of Halogenated HC The pathway Meta cleavage: