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

## TL;DR

This study shows how adjusting oxygen and carbon levels in bacterial cultures can control the composition of a biodegradable polymer, useful for biomedical applications.

## Contribution

The study demonstrates a novel method to tailor the 3HV fraction in P3HBV by manipulating oxygen and carbon limitations in continuous cultures.

## Key findings

- Oxygen limitation increased biomass and P3HBV concentrations to 3.3 g L−1 and 2.1 g L−1, respectively.
- The highest 3HV molar fractions (33.7 and 36.4 mol %) were observed at the lowest and highest oxygen uptake rates.
- An elevated NAD(P)H/NAD(P)+ ratio under oxygen limitation favored polymer accumulation.

## Abstract

Azotobacter vinelandii OP is a bacterium that can produce poly(3-hydroxybutyrate-co-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 (qO2) in chemostat cultures of A. vinelandii OP. Steady-state conditions with either oxygen or carbon limitation were established by modulating the agitation rates. Under oxygen-limited conditions (low qO2 values) biomass and P3HBV concentrations increased to 3.3 g L−1 and 2.1 g L−1, respectively. At higher qO2 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 qO2 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 Azotobacter vinelandii OP. Such insights can support the development of tailored bioprocesses to modulate polymer characteristics, enabling a broader range of potential biomedical applications for P3HBV.