Effect of sodium accumulation on heterotrophic growth and polyhydroxybutyrate (PHB) production by Cupriavidus necator

• A mechanistic model was developed to evaluate the effect of Na+ on PHB production.
• Model calibration and validation was performed with batch and fed-batch data sets.
• Both the steady state and dynamic behavior was effected by Na+.
• Non-linear inhibition effect of Na+ on growth and PHB content.
• Na+ shows linear inhibition effect on PHB production rate.

This study evaluates the effect of sodium (Na+) concentration on the growth and PHB production by Cupriavidus necator. Both biomass growth and PHB production were inhibited by Na+: biomass growth became zero at 8.9 g/L Na+ concentration while PHB production was completely stopped at 10.5 g/L Na+. A mathematical model for pure culture heterotrophic PHB production was set up to describe the Na+ inhibition effect. The parameters related to Na+ inhibition were estimated based on shake flask experiments. The accumulated Na+ showed non-linear inhibition effect on biomass growth but linear inhibition effect on PHB production kinetics. Fed-batch experiments revealed that a high accumulation of Na+ due to a prolonged growth phase, using NaOH for pH control, decreased the subsequent PHB production. The model was validated based on independent experimental data sets, showing a good agreement between experimental data and simulation results.