Lignin Aromatics to PHA Polymers: Nitrogen and Oxygen Are the Key Factors for Pseudomonas

Abstract

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.

Microbial Valorization of Lignin to Bioplastic by Genome-Reduced Pseudomonas putida

“…A highly viscous medium may adversely affect the dissolution and diffusion of oxygen, hindering lignin metabolism and PHA synthesis ( Liu et al, 2018 ). In addition, aromatic derivatives possessing aldehyde and methoxy groups may enhance the inhibitory effects on the P. putida cells and lead to poor PHA accumulation ( Shin et al, 2019 ; Ramirez-Morales et al, 2021 ). Furthermore, the salt concentration in APL from alkaline fractionation was increased and could be harmful to cell growth and PHA accumulation.…”

Valorization of Lignocellulose by Producing Polyhydroxyalkanoates under Circular Bioeconomy Premises: Facts and Challenges

“…However, lignocellulosic biorefineries have traditionally exploited the carbohydrates fraction to generate biofuels and chemicals, while the valued lignin fraction has remained as underutilized waste . Recently, advances in synthetic biology and metabolic engineering biological valorization of lignin has become possible, as, in some microorganisms, metabolic pathways have been constructed for the conversion of heterogeneous phenolics via biological funneling to value-added products such as PHAs. ,− Utilizing lignocellulose may become a promising, greener, economic, and sustainable approach to PHA production (Table ), as resources are not in direct competition with food values. , …”

Optimized pulse‐feeding fed‐batch fermentation for enhanced lignin to polyhydroxyalkanoate transformation

“…showing the effects of C:N ratio on stimulating PHA synthesis. 20,22 However, further increase in feed volume could better enhance PHA accumulation than further increase in C:N ratio as shown in the effect of the quadratic (Q) term for both factors. This suggested that a very high C:N ratio may not increase the production of PHA, potentially due to the negative effect inserting on cell growth.…”

“…19 Recently, a milestone of PHA development from lignin has been accomplished through the optimization of bioprocess. 20 Effects of C:N ratio and aeration on mcl-PHA production were examined leading to high PHA titer (approximated 0.5 g/L) from lignin through batch process optimization. Enhanced lignin to PHA conversion would be very likely if fedbatch strategy was further implemented in process optimization.…”