Tailoring 3HV Fraction in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Azotobacter vinelandii Through Oxygen and Carbon Limitation in Continuous Cultures

<i>Azotobacter vinelandii</i> OP is a bacterium that can produce poly(3-hydroxybutyrate-<i>co</i>-3-hydroxyvalerate) (P3HBV), a biodegradable and biocompatible polymer with applications in the biomedical field. This study aimed to evaluate P3HBV production and its 3-hydroxyvalerate (3HV) fraction under different agitation rates and oxygen uptake rates (q_O2) in chemostat cultures of <i>A. vinelandii</i> OP. Steady-state conditions with either oxygen or carbon limitation were established by modulating the agitation rates. Under oxygen-limited conditions (low q_O2 values) biomass and P3HBV concentrations increased to 3.3 g L^-1 and 2.1 g L^-1, respectively. At higher q_O2 values, the chemostat cultures were limited by carbon, and P3HBV content decreased from 62% to 33% (w w^-1). The highest 3HV molar fractions, 33.7 and 36.4 mol %, were observed at both the lowest and highest q_O2 levels, possibly linked to comparable valeric acid consumption rates. An elevated NAD(P)H/NAD(P)⁺ ratio was also observed under oxygen limitation, favoring polymer accumulation by indicating a more favorable intracellular redox state. These findings highlight the impact of nutrient limitation and respiratory activity on the biosynthesis of P3HBV and the 3HV composition by <i>Azotobacter vinelandii</i> OP. Such insights can support the development of tailored bioprocesses to modulate polymer characteristics, enabling a broader range of potential biomedical applications for P3HBV.