초록
<P>Muconic acid (MA) is a bio-based platform chemical that can be converted into the commodity petrochemical building blocks adipic acid or terephthalic acid, or used in emerging, performance-advantaged materials. MA is a metabolic intermediate in the β-ketoadipate pathway, and can be produced from carbohydrates or other traditional carbon sources <I>via</I> the shikimate pathway. MA can also be produced from lignin-derived aromatic compounds with high atom efficiency through aromatic-catabolic pathways. Metabolic engineering efforts to date have developed efficient muconic acid-producing strains of the aromatic-catabolic microbe <I>Pseudomonas putida</I> KT2440, but the titers, productivities, and yields from aromatic compounds in most cases remain below the thresholds needed for industrially-relevant bioreactor cultivations. To that end, this work presents further process and host development towards improving MA titers, yields, and productivities, using the hydroxycinnamic acids, <I>p</I>-coumaric acid and ferulic acid, as model aromatic compounds. Coupling strain engineering and bioprocess development enabled the discovery of new bottlenecks in <I>P. putida</I> that hinder MA production from these compounds. A combination of gene overexpression and removal of a global catabolic regulator resulted in high-yielding strains (100% molar yield). Maximum MA titers of 50 g L<SUP>−1</SUP>, which is near the lethal toxicity limit in this bacterium, and productivities over 0.5 g L<SUP>−1</SUP> h<SUP>−1</SUP> were achieved in separate process configurations. Additionally, a high-pH feeding strategy, which could potentially reduce the salt load and enable higher titers by decreasing product dilution, was tested with model compounds and lignin-rich streams from corn stover and a complete conversion of the primary monomeric aromatic compounds to MA was demonstrated, obtaining a titer of 4 g L<SUP>−1</SUP>. Overall, this study presents a step forward for the production of value-added chemicals from lignin and highlights critical needs for further strain improvement and bioprocess development that can be applied in the biological valorization of lignin.</P><P>Graphic Abstract</P><P>This work shows parallel strain and bioreactor process development to improve muconic acid production from aromatic compounds and lignin.<BR/><IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c8gc02519c'/><BR/></P>