Studies On The Selection Of High-yield PHB Strains By Protoplast Technology And Its Fermentation Conditions

Poly- -hydroxybutyrate(PHB) is a microbial polyester which is accumulated in certain bacteria. It crystallizes to form a polymer with similar properties to polypropylene. PHB is also biodegradable and biocompatibile. PHB as raw material of bioplatics is investigative hot point recently. But the high fermentation cost is one of the disad-vantage facters in the industrialization production. The main solution to the above problems includes:(l) breed the high-yield strain; (2) use the low-price raw material; (3) optimize the process of PHB synthesize; (4) develop the proper distill method.Objective: Breed selectively the high-yield strain to increase the yield of PHB. Methods: selecting two strains with great difference in physiology characteristics and appearances as starting strains; proceeding the protoplasm fusion and laser treatment. On the condition, the condition of shaking-flask was optimized. Result: By taking S-8 and Q-72 as starting strains, the two parental strains were hydrolyzed by lyticase. The rate of protoplast formation of strain S-8 was 78.0% while the rate of regeneration 19.5%; the rate of protoplast formation of strain Q-72 was 96.0% while the rate of regeneration 31.4%. The protoplast of the two parental strains were killed by heating and UV, respectively, then the protoplasts was fused by PEG. Fusant strains could be selected, the Fusant strain R-7 is stabled, its PHB yield could be improved obviously than the starting strains. At the same time, The mutant strains could be selected by laser treatment with strain S-8 as starting strain. Compared with S-8, the highest PHB production of strainY-l 7 amount to 4.86g/L. Its PHB yield increased by 67.0% than strain S-8. In addition, the ingredient of the fermention medium of Y-17 were optimized, the Y-17 can accumulate PHB 5.82g/L under the optimum condition. Then, feeding the carbon source, nitrogen source and H2O2 in the Fed-Batch-Process, PHB production improve greatly, amount up to 10.93 g/L. Conclusion: The properties of mutated strain Y-17 could accord with the demands of industrial production, it has important industrial application prospect as good fermentation strains.