Study On Mutation Breeding And The Fermentation Technological Conditions For The Bacteria Producing Polyhydroxyalkanoates

Biodegradable plastics are the ideal alternative to conventional plastics, one of the biodegradable plastics is Polyhydroxyalkanoates (PHAs). The primary means of production in PHA is microbial fermentation, which was a hot topic in biodegradable plastics.In this paper, we use the conserved stains that can produce PHA from our laboratory. After severals filtration, we selected the strain M-12 which was acted as initial strain. M-12 was mutated by NaN02, UV and both of them to increase PHA production. The results showed that the mutant strain UY-7 which had better hereditary stability when the coordinative effect of UV and NaNO2. The cell dry weight of the strain UY-7 was 9.68g/L, 47% higher than initial strain M-12(6.59g/L); the concentration of PHA was 4.37g/L,126% higher than M-12(1.93g/L).This experiment optimized the culture conditions of the mutation strain UY-7. Sugar and (NH4)2SO4, yeast extract, beef paste acted as the best carbon and nitrogen substrates for the production of PHA. The L9(34) ort-hogonal experiment was used to optimized fermentative condition. The result showed that the optimum medium which sugar concentration was 30g/L, nitrogen concentration was 0.3%(NH4)2SO4 and 0.2% yeast extract and 0.2% beef paste were adopted. The optimum fermentative conditions were the initial pH 7.0, the medium volume 70mL/250mL, temperature 30℃, bacterium age 18h, the inoculation 15%. The best supplemented medium fermentation condition in shake bottle was as follows:2.5% sugar concentration controlled,0.25% NH4+concentration controlled, supplemented medium time was that carbon substrates from 12h to 24h in every 4h; and nitrogen substrates at 8h,16h. The cell dry weight of strain UY-7 increased to 24.3g/L, the PHA concentration of increased to 12.1g/L.Based on the flask results, we studied the batch and supplemented medium fermentation in fermentor. The best fermentative conditions in fermentor were medium volume 4L, air fluidlv/vm, moving velocity was varied from 300r/min to 450r/min according to fermentation. The best supplemented medium fermentation conditions in fermentor was as follows:2.5% sugar concentration controlled,0.25% NH4+concentration controlled, supplemented medium fermentation time in fermentor was that carbon substrates from 8h to 28h in every 4h and nitrogen substrates at 8h,16h. The cell dry weight of strain UY-7 increased to 38.5g/L, the PHA concentration of strain UY-7 increased to 18.8g/L. After optimization, the strain UY-7 was improved greatly in cell dry weight and PHA production. It can provide thereunder for magnified culture and it would be implemented in PHA industrialization.