Round Brown Nitrogen-fixing Bacteria, G-3 Strains Synthesis Of 3 - Hydroxy Butyric Acid 3 - Hydroxyvalerate Copolymer Fermentation Conditions Study

Production of the bioplastic poly(3 -hydroxybutyrate - co-3 -hydroxyVa1 erate )(PHBV) by Azotobacter chroococcum G-3 was investigated under fiask culture and2-liter fermentor fed-batch culture conditions. PHBV was Produced when valetalewas suPplied as an auxiliary carbon source, with sucrose as the main carbon source.Sucrose concentration of l-2% and high dissolved oxygen (DO) concentrationpromOted cell grOwth, while sucrose conceIltration of 3-4% and oXygen limitationstimulated PHBV accumulation. The optimal iintial addition time of vaIerate wasdetermined at the onset of PHBV formation period. Although relatively high H'V unitcould be Obtained under high valerate concentration, the growth and Product Syntheticactivities was idebited obviously PHBV of different HV fraction could be obtainedby changing the conceamion of valeat. In 2-L fermentor, with different ratios ofsucrose to valerate feeding, vallable DO concentraion and PH, the cell tw weighand the HV fraction in PHBV was l2.7-17'2g/L and l3.2-24.5mol%, respectively.The PHBV content maintained more than 68% of the dry cell weigh.Polysaccharide Produced by A. chrOococcum caused an increase in viscosity andthe low conversion frOm subStraes to PHBV This problem was successfully solvedby the mixed culfore fermentaion of Bacillus megaterium G-6 and A. chroococcumG-3. Furthermore, the aPPlication of stheh as a cosubstrate in the mixed culturefermentyion was confirmed suitable. PHBV PrOduction imProved greatly Whenaddtion the amoun of subStraes feeding. The final cell dry weigh. PHBV content,and HV fraction in PHBV reached 36.6g/L, 74% and l5mol%.The results of the thermal and mechanical properties tests of PHBV showed thatthe PHBV PrOduct possessed better properties than PHB and was consistent with theintemational quality standard in PHA engineering.