Abstract
BackgroundCis, cis-muconic acid (MA) is a dicarboxylic acid of recognized industrial value. It provides direct access to adipic acid and terephthalic acid, prominent monomers of commercial plastics.ResultsIn the present work, we engineered the soil bacterium Corynebacterium glutamicum into a stable genome-based cell factory for high-level production of bio-based MA from aromatics and lignin hydrolysates. The elimination of muconate cycloisomerase (catB) in the catechol branch of the β-ketoadipate pathway provided a mutant, which accumulated MA at 100% molar yield from catechol, phenol, and benzoic acid, using glucose as additional growth substrate. The production of MA was optimized by constitutive overexpression of catA, which increased the activity of the encoded catechol 1,2-dioxygenase, forming MA from catechol, tenfold. Intracellular levels of catechol were more than 30-fold lower than extracellular levels, minimizing toxicity, but still saturating the high affinity CatA enzyme. In a fed-batch process, the created strain C. glutamicum MA-2 accumulated 85 g L−1 MA from catechol in 60 h and achieved a maximum volumetric productivity of 2.4 g L−1 h−1. The strain was furthermore used to demonstrate the production of MA from lignin in a cascade process. Following hydrothermal depolymerization of softwood lignin into small aromatics, the MA-2 strain accumulated 1.8 g L−1 MA from the obtained hydrolysate.ConclusionsOur findings open the door to valorize lignin, the second most abundant polymer on earth, by metabolically engineered C. glutamicum for industrial production of MA and potentially other chemicals.
Highlights
Cis, cis-muconic acid (MA) is a dicarboxylic acid of recognized industrial value
Deletion of muconate‐cycloisomerase enables MA production from small aromatics In order to block the catabolization of small aromatics at the level of MA, the gene encoding for muconate-cycloisomerase (catB) gene encoding muconatecycloisomerase, was deleted from the genome of the wildtype C. glutamicum ATCC 13032
In contrast to the wild type, the MA-1 strain was no longer able to grow on the aromatic compounds benzoic acid, catechol, and phenol as sole carbon source
Summary
Cis-muconic acid (MA) is a dicarboxylic acid of recognized industrial value. It provides direct access to adipic acid and terephthalic acid, prominent monomers of commercial plastics. Adipic acid and terephthalic acid have wide applications in the cosmetic, Different microorganisms, such as Pseudomonas putida KT2440 [4], Amycolatopsis species ATCC 39116 [15], and E. coli [5] have been engineered to produce MA either via biosynthesis from glucose [6,7,8] and glycerol [2] or via biotransformation from aromatics [9,10,11]. The latter is advantageous, because it requires only a few biochemical reactions and offers molar yields up to 100% [4]. MA production has been demonstrated for different aromatics, including
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