Modelling growth-arrested production of polyhydroxybutyrate by Cupriavidus necator DSM 545

Abstract

Production of polyhydroxyalkanoates has gained attention because they are biobased and biodegradable plastics. Among them, polyhydroxybutyrate (PHB) is the most common type of polyhydroxyalkanoate produced by several bacteria including Cupriavidus necator. Hence, this work aims to use resting cells of C. necator DSM 545 because this strategy is simpler than culture processes and this strain can assimilate glucose, a widely available monomer. C. necator DSM 545 was grown using a defined culture medium. The biomass was harvested and utilized to carry out resting cells experiments using phosphate buffer amended with glucose in different concentrations (2–20 g/L). Additional experiments include tests with different cell concentrations (1–8 g/L), shaking rates (150 and 180 rpm), and measurement of dissolved oxygen in 250 mL Erlenmeyer flasks to determinate the volumetric mass transfer coefficient. Experiments with resting cells showed PHB production while the PHB-free biomass remains constant. The glucose uptake rate has a lineal behavior regarding initial PHB-free biomass (q_S=0.37 ± 0.01 g_glucose/g_{PHB-free biomass}·h) and a saturation trend regarding glucose concentration (K_S=0.88 ± 0.05 g/L). The observed yield for PHB was 0.482 ± 0.003 g_PHB/g_glucose (Y_P/S), coinciding with the maximum reported for the metabolic route. Measurements of dissolved oxygen showed that the process may be limited by the oxygen transfer rate.