Pilot-scale production of mcl-PHA by Pseudomonas citronellolis using acetic acid as the sole carbon source

Medium-chain-length polyhydroxyalkanoates (mcl-PHA) are biobased materials with promising properties for environmentally friendly applications. Due to high production costs, which are related to the cost of the carbon sources combined with conversion insufficiencies, currently only small quantities are produced. This results in a lack of reliable data on properties and application potential for the variety of polymers from different types of production strains. This study investigated the potential for the production of mcl-PHA from volatile fatty acids (VFA) at a larger scale, given their potential as low-cost and sustainable raw material within a carboxylateplatform based biorefinery. Pseudomonas citronellolis (DSMZ 50332) was chosen as the production strain, and acetic acid was selected as the main carbon and energy source. Nitrogen was limited to trigger polymer production, and a fed-batch process using a pH-stat feeding regime with concentrated acid was established. We report successful production, extraction, and characterization of mcl PHA, obtaining a total of 1.76 kg from two 500-litre scale fermentations. The produced polymer was identified as a copolymer of 3-hydroxydecanoate (60.7%), 3-hydroxyoctanoate (37.3%), and 3-hydroxyhexanoate (2.0%) with a weight average molecular weight (Mw) of 536 kDa. NMR analysis indicates the presence of unsaturated side chains, which may offer additional possibilities for modification. The results confirm that there is a potential to produce significant amounts of mcl-PHA with interesting rubber-like properties from waste-derived VFA.

Automated summary

This study investigated the potential for large-scale production of mcl-PHA using volatile fatty acids (VFA). By adjusting nitrogen concentration and using a pH-stat feeding regime, a significant amount of high-quality mcl-PHA was successfully produced. The results demonstrate that waste-derived VFA can be used to produce mcl-PHA with rubber-like properties.