Microrespirometric validation of a two-stage process for polyhydroxyalkanoates production from peanut oil and propionate with cupriavidus necator

Poly(3-hydroxyalkanoates) (PHA) are biodegradable polyesters produced by various bacteria, including Cupriavidus necator. The composition of PHA depends on the type of microorganism, cultivation conditions, and carbon substrate used. Selecting the right carbon source is crucial for PHA production as it greatly affects the process costs. Therefore, scalability is a common goal, and the design and optimization of PHA production rely on experimentally determining key parameters.

In this study, we used a two-stage process for PHA production in shaking flasks acting as mini reactors with Cupriavidus necator. In the first stage, fructose was the sole carbon source. After the fructose was depleted, a second stage began with either peanut oil or propionate as the new carbon source to enhance PHA production. We used an ex-situ pulse respirometry approach during the two-stage process to monitor substrate consumption kinetics.

The findings showed that using peanut oil was more beneficial than propionate, leading to a 12.2% increase in biomass and a 13.9% increase in PHA production.

Moreover, the growth rate was 88.9% higher with peanut oil. The pulse respirometry technique applied in microreactors, known as microrespirometry, enabled up to 216 biological experiments to determine four important kinetic and stoichiometric parameters: maximum oxygen uptake (rO2max), substrate affinity constant (KS), growth yield (YX/S), and substrate oxidation yield (YO2/S). These parameters indicated that peanut oil is the best carbon source for promoting PHA production in the second stage. Using microrespirometry for screening carbon sources for PHA production provided reliable information quickly and with significantly less experimental effort.

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