This work aimed to investigate the optimal conditions for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or PHBV production by the newly isolated Bacillus megaterium P-12. The optimal growth condition of B. megaterium P-12 was 37℃ in Basal Culture Medium (BCM) adjusted initial pH at 7.0. The maximum dry cell weight (DCW) obtained was 6.15 gL⁻¹ at 12 h of cultivation. The effect of sugar used as a carbon source on cell growth and poly(3-hydroxybutyrate) or P(3HB) synthesis was examined in order to investigate an inexpensive carbon source. The results showed that B. megaterium P-12 produced the highest DCW of 3.26 gL⁻¹ and P(3HB) content of 56.64 % DCW in the production medium containing sucrose at 18 h of cultivation. To reduce the production cost, using an inexpensive carbon source is one of the alternative solutions. Sugarcane liquor is a good candidate due to its high sugar content (mainly sucrose). When B. megaterium P-12 was cultivated in the production medium containing 20.0 gL⁻¹ of total sugar in sugarcane liquor, the maximum P(3HB) content was 56.46 % DCW comparable to that with sucrose but higher DCW of 9.22 gL⁻¹ and shorter cultivation time at 6 h. For PHBV production, sugarcane liquor and sodium valerate were used as 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) generating carbon source, respectively. The suitable mole fraction of 3HV at 21 mol% was determined in the medium containing 10.0 gL⁻¹ of total sugar (in sugarcane liquor) and 10.0 gL⁻¹ of sodium valerate as the mixed carbon source with 1.0 gL⁻¹ of urea as a nitrogen source. The highest DCW of 3.78 gL⁻¹ and PHBV content of 37.06 % DCW were detected at 12 h of cultivation. The higher yield of cell mass and PHBV were obtained in 5 L fermenter compared to that of shake flask culture i.e. cell concentration was 4.89 gL⁻¹ and PHBV content was 41.36 % DCW. Some of physicochemical properties of PHBV were as followed: melting temperature of 143.44 ℃, glass transition temperature of -17.09 ℃ and molecular weight of 6.53 x 10⁵ Da, respectively.
