Lignin aromatics to PHA polymers: Nitrogen and oxygen are the Key factors for Pseudomonas.
Many wild type Pseudomonas strains have the potential to contribute to the valorization of lignin in future biorefineries. Through a robust aromatic catabolism, i.e., biofunneling capacity, they can ease the inherent aromatic heterogeneity found in lignin hydrolysates and accumulate naturally marketable biopolymers like mcl-polyhydroxyalkanoate (mcl-PHA) under nitrogen limitation. Besides a comparative strain evaluation, we present fundamental research on the funneling of aromatic mixtures under specific bioprocess conditions to improve biocatalytic lignin valorization. For the most robust and best performing strain, P. putida KT2440, we improve the mcl-PHA accumulation from a defined aromatic mixture of p-coumarate, ferulate, and benzoate under technically relevant conditions by up to 40% by tailoring the nitrogen and oxygen supply. The highest mcl-PHA concentration (582 ± 41 mg L–1) was obtained for a C/N ratio of 60 for oxygen-unlimited conditions (oxygen transfer rate >20 mmol L–1 h–1). In contrast, aromatic intermediates accumulated under oxygen-limited conditions at oxygen transfer rates below 10 mmol L–1 h–1. The experimental conditions were scalable into a 1L stirred tank bioreactor. This study contributes to deepening our understanding of the biocatalytic capability of promising Pseudomonas strains toward downstream microbial conversions of lignin aromatics for future biorefinery applications.