Media Optimization for Poly(β-hydroxybutyrate) Production Using Azotobacter Beijerinckii

In the present study, efforts were made to optimize the growth of Azotobacter beijerinckii in the media with essential nutrients for production of PHB. The effects of temperature, agitation rate, carbon and nitrogen source concentrations on microbial grows and PHB production were investigated. Glucose and ammonium chloride were used as carbon and nitrogen source, respectively. The optimal temperature for the growth and PHB synthesis appeared to be 30 degrees C. However, over the range of 25-38 degrees C, the effect of temperature was not very significant. Fermentation under controlled conditions such as agitation rate of 250rpm, incubated inoculums for 15h, fermentation temperature at 30 degrees C, and fermentation time of 72h was performed. Glucose concentration of 30 to 60g/l with increment of 10g/l and ammonium chloride in the range of 0.5 to 2g/l with increment of 0.5g/l were utilized as carbon and nitrogen sources, respectively. The PHB production was maximized at the desired concentration of glucose (50g/l) and ammonium chloride (1.5) for carbon and nitrogen sources, respectively. A. beijerinckii exhibited maximum biomass of 17.31g/l with a PHB concentration of 5.84g/l. Under the best conditions, PHB constituted up to 34% of dry cell mass after 64h of culture. The average biomass yield coefficient on glucose was about 0.57kg/kg.