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Title of Thesis

Aamer Ali Shah
Institute/University/Department Details
Department of Microbiology/ Quaid-i-Azam University, Islamabad
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
microorganisms, biodegradation, plastics, polyethylene, polyurethane, low density polyethylene

The present study was aimed to isolate the microorganisms from soil, with the ability to degrade plastics including Polyethylene, Polyurethane, Poly(3-hydoxybutyrate) (PH B) and Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), observe the extent of degradation by analysis of plastics and study of enzymes involved in the process of degradation.

Low density polyethylene (LOPE) is one of the major sources of environmental pollution. In the present study, the pieces of LOPE plastic bags were buried in soil and observed microscopically after 10 months. Fungal strains found attached on the surface of LOPE plastic pieces were identified as Fusarium sp. AF4, Aspergillus terreus AF5 and Penicillium sp. AF6. Scanning electron microscopy (SEM) showed some mechanical damage or erosions on the surface of LOPE pieces incubated with Fusarium sp. AF4. Biodegradation of LOPE was determined by Sturm test, and it was found that in case of test the total amount of C02 produced was 1.85 g/l and in control it was 1.45 g/l. No changes in the Fourier Transform Infrared Spectroscopy (FTIR) were observed after soil burial of LOPE film. Further the possibility of accelerating the biodegradation process by exposing LOPE pieces to UV radiation and treating with nitric acid before microbial treatment. FTIR analysis of the pretreated PE pieces showed some breakdown indicated by the change in spectra at the wavelength 1710 cm-1 and 831 cm-1 which decreased to 1708 cm-1 and 830 cm-1.

Bacterial strains attached on the Polyurethane (PU) film, after soil burial for 6 months, were isolated and identified as Bacilllus sp. AF8, Pseudomonas sp. AF9. Micrococcus sp. AF10, Arthrobacter sp AF11, and Corynebacterium sp. AF12. Hydrolytic zones were observed around the colonies of the bacterial isolates when plated on PU-containing mineral salt media. SEM of the PU films after microbial treatments showed pits, extensive spotting and change in color. FTIR analysis also showed the formation of some new intermediate products. The results of the Sturm test showed more CO2 production (4.46 g/l) than that in the control (2.23 g/l), when PU was degraded by bacterial consortium of the isolates.

Poly(3-hydroxybutyrate) (PHB) and Poly(3-hydroxybutyrate-co-3-hyroxyvalerate) (PHBV) degrading actinomycete strain, Streptoverticillium kashmirense AF1, was isolated from soil by enrichment technique. The degradation of PHB and PHBV by Stv. kashmirense AF1 was studied by observing the formation of clear zones of hydrolysis on the polymer containing mineral salt agar plates. The optimum production of the PHB and PHBV depolymerases was observed both at slightly alkaline and neutral pH (pH 8 and pH 7), 45°C, 1 % substrate concentration and in the presence of lactose as an additional carbon source. Two types of PHB and PHBV depolymerases were purified by column chromatography using Sephadex G-75 and their molecular weights were determined as 37 and 45 kDa and 35 and 45 kDa, respectively, by SOS-PAGE. In case of microbially treated PHB and PHBV, the FTIR spectra showed formation of some new peaks (1400-1600 cm-1). In case of PHB degradation, the Sturm test showed amount of CO2 evolved in test (6.02 g/l) was more as compared to the control (2.99 g/l). Positive degradation was also shown by the amount of CO2 evolved in case of PHBV Sturm test (7.85 g/l, test; 0.94 g/l, control).

Three PHBV degrading bacterial strains identified as Bacillus subtilis AF2, Bacillus megaterium AF3, Micrococcus sp. AF7 were isolated after soil burial of PHBV film for about 120 days. The bacterial strains found to degrade PHBV film, produced clear zones of hydrolysis on the PHBV containing agar plates when used in the form of consortium. The PHBV degraders showed optimum depolymerase production at pH 7, 37oC, in the presence of 0.4% substrate, and presence of glucose and Tween 80 during 2-5 weeks of incubation. Bacillus megaterium AF3 was found to produce more PHBV depolymerase than the other members of the consortium. PHBV depolymerase was purified from B. megaterium AF3to homogeneity by chromatography on Sephadex G-75 and its molecular weight was found to be approximately 37 kDa. Sturm test also indicated the degradation of PHBV by bacterial consortium.

Download Full Thesis
5097.13 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
411.44 KB
2 1 Introduction
463.26 KB
  1.1 History Of Plastics 1
  1.2 Plastics And Their Uses 2
  1.3 Disposal Of Plastics 6
  1.4 Hazards Of Plastics 7
  1.5 Degradation Of Plastics 8
  1.6 Research Objectives 17
3 2 Literature Review
1148.27 KB
  2.1 Plastics 18
  2.2 Application Of Biodegradable Plastics 20
  2.3 Production Of Plastics 24
  2.4 Hazards Of Plastics 26
  2.5 Plastic Waste Disposal/Management 29
  2.6 Degradation Of Plastics 33
  2.7 Biodegradability Testing 51
4 3 Materials And Methods
517.62 KB
  3.1 Materials/Chemicals 59
  3.2 Media For Cultivation And Degradation Experiments 59
  3.3 Microorganisms 59
  3.4 Sample Collection 62
  3.5 Total Colony Count 62
  3.6 Isolation Of Plastic Degrading Microorganisms 62
  3.7 Identification Of The Selected Isolates 64
  3.8 Biodegradation Studies 66
  3.9 Statistical Analysis 81
5 4 Results
1051.78 KB
  4.1 Isolation And Identification Of Plastic Degrading Microorganisms 83
  4.2 Biodegradation Of Synthetic Plastics 91
  4.3 Biodegradation Of Natural Plastics 102
  4.4 Production Of Poly( 3-Hydroxybutyrate) And Poly(3-Hydroxybutyrate-Co-3-Hyroxyvalerate) 112
  4.5 Statistical Analysis 128
  4.6 Production And Purification Of Production Of Poly( 3-Hydroxybutyrate) And Poly(3-Hydroxybutyrate-Co-3-Hydroxybutyrate) 130
6 5 Discussion 138
502.95 KB
7 6 Conclusions 153
28.84 KB
8 7 Future Prospects 154
28.22 KB
9 8 References 155
755.6 KB
10 9 Appendix 187
278.6 KB
11 10 Publications 208
200.96 KB