Composition control of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymerization by oxygen transfer rate (OTR) in Azotobacter vinelandii OPNA

BACKGROUND: The aim of this study was to evaluate changes in the composition of poly-3-hydoxybutyrate-co-3-hydroxyvalerate (PHBV) by the polyhydroxybutyrate (PHB) overproducing mutant OPNA of Azotobacter vinelandii cultured under different conditions. RESULTS: The oxygen transfer rate (OTR) significantly affected PHBV composition in cultures in shaken flasks; the highest content of 3-hydroxyvalerate (3HV; 28%) was achieved from cultures developed at an OTR_max of 5.87 mmol L⁻¹ h⁻¹. In the bioreactor, cultures were grown under oxygen-limited conditions and different OTRs, varying the agitation rate. The highest PHBV accumulation (85%) was achieved at a low OTR_max (4.96 mmol L⁻¹ h ⁻¹), whereas the maximum content of 3HV (8.5 mol%) was obtained at a higher OTR_max (20.3 mmol L⁻¹ h⁻¹). The OPNA strain produced a copolymer of ultra-high molecular weight. CONCLUSIONS: Our results reveal that increasing the OTR_max raises the molar fraction of 3HV in the PHBV copolymer. Therefore, the manipulation of OTR could be a feasible strategy to produce PHBV copolymers with different monomeric compositions at industrial level.