Studies On Fermentation Conditions For The Production Of Polyhydroxyalkonates By Azotobacter Chroococcum G-3

Production of the biodegradable plastic ?polyhydroxyalkonates(PHA) by Azotobacter chroococcum G-3 was investigated under flask culture and 2-liter fermentor conditions . The results showed that sucrose is the best carbon source , and the 0.1% peptone is the best nitrogen source for this strain . On the basis of analysis of batch fermentation results, the fed-batch culture for PHA production was carried out in a 2L fermentor.The CDW and PHA yield could reach 38.4g/L and 29.6g/L at 32h ,respectively. Under the control of exponential fed-batch model,26.5g/L of CDW and 20.7g/L of PHA yield could be achieved at 28h,respectively.Polysaccharide produced by Azotobacter chroococcum G-3 caused an increase in viscosity and the low conversion from substrates to PHA. This problem was successfully solved by the mixed culture fermentation of Bacillus megaterium G-6 and Azotobacter chroococcum G-3. Combined with the fed-batch culture, The CDW and PHA yield could reach 47.8g/L and 38.2g/L.The molecular weight of the PHA was affected by different ways.The influence of C/N ratio and the recovery methods on the molecular weight change were investigated.The addition of 4%(v/v)PEG(Mn=200g/mol,PEG-200) to the fermentation broth of strain Azotobacter chroococcum G-3 resulted in chain termination through esterification at the carboxyl terminus of the PHA with PEG chain segments,thus reducing the molar mass from 1.33 X 106 to 5.1 X 104.