Extended batch cultures for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production by Azotobacter vinelandii...

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a polymer produced by Azotobacter vinelandii OP. In the bioreactor, PHBV production and its molar composition are affected by aeration rate. PHBV production by A. vinelandii OP was evaluated using extended batch cultures at different aeration rates, which determined different oxygen transfer rates (OTR) in the cultures. Under the conditions evaluated, PHBV with different 3-hydroxyvalerate (3HV) fractions were obtained. In the cultures with a low OTR (6.7 mmol L^-1 h^-1, at 0.3 vvm), a PHBV content of 38% w w^-1 with 9.1 mol % 3HV was achieved. The maximum PHBV production (72% w w^-1) was obtained at a high OTR (18.2 mmol L^-1 h^-1, at 1.0 vvm), both at 48 h. Thus, PHBV production increased in the bioreactor with an increased aeration rate, but not the 3HV fraction in the polymer chain. An OTR of 24.9 mmol L^-1 h^-1 (at 2.1 vvm) was the most suitable for improving the PHBV content (61% w w^-1) and a high 3HV fraction of 20.8 mol % (at 48 h); and volumetric productivity (0.15 g L^-1 h^-1). The findings indicate that the extended batch culture at 2.1 vvm is the most adequate mode of cultivation to produce higher biomass and PHBV with a high 3HV fraction. Overall, the results have shown that the PHBV production and 3HV fraction could be affected by the aeration rate and the proposed approach could be applied to implement cultivation strategies to optimize PHBV production for different biotechnological applications.