Breeding Of Bacillus Megaterium To Degrade PLA And The Research Of PLA De-polymerase

Along with the increased to plastic products demand, it has brought the noticeabl e energy crisis and the environment crisis. The ordinary plastic cannot be degraded in the natural environment for decades, therefore it is important to develop biodegradabl e plastic.The development of biodegradable plastic mainly include polyesters, among all polyesters, poly(L-Lactic acid) (PLA) is especially promising with its excellent physicochemical properties and the potential price benefit. Although PLA has distinct advantages in production and application over other polyesters, the study of its biodegradation is relatively lagging behind its synthesis. In this thesis, we screening and appraisal from strains, determine the optimal conditions of producting enzyme , isolate and purify of PLA—degrading enzymes. The major results of the thesis are as follows:1. Poly (L-lactic acid) (PLA)-degrading strain, was isolated by screening activated sludge produced from Fu shun petroleum factory. The PLA strain is numbered for DS04 - W.2. The DS04—W is observed on morphological, physiological and biochemical properties mensuration, and determine 16S rDNA sequence. Finally the DS04—W is identified the bacterium Bacillus megaterium.3.The DS04—W bacteria is determined the degradation ability of PLA film. The PLA film shape is observed with scanning electron microscopy. We found transparency gradually declined, surface become coarse, and visible to subtle vesicles swelled in degradation process. The result shows that the DS04 - W strains of PLA has the degradation ability of PLA film.4. The optimal conditions of production PLA—degrading enzyme is determined. First we should choose the best inductor from gelatin, yeast powder, casein tyrosine, according to the result of the experiment selected for yeast powder for inductor. Second we determine the temperature, pH , wave bed RPM, inoculation amount. Finally, through four factors of three levels orthogonal experiment, we determine the optimal fermentation conditions are 48h for training time, culture medium for 8.5, starting pH wave bed 200r/min, speed for seed medium inoculated quantity 6% (V/V).