Abstract
Bio-based plastics represent an increasing percentage of the plastics economy. The fermentative production of bioplastic monomer 5-aminovalerate (5AVA), which can be converted to polyamide 5 (PA 5), has been established in Corynebacterium glutamicum via two metabolic pathways. l-lysine can be converted to 5AVA by either oxidative decarboxylation and subsequent oxidative deamination or by decarboxylation to cadaverine followed by transamination and oxidation. Here, a new three-step pathway was established by using the monooxygenase putrescine oxidase (Puo), which catalyzes the oxidative deamination of cadaverine, instead of cadaverine transaminase. When the conversion of 5AVA to glutarate was eliminated and oxygen supply improved, a 5AVA titer of 3.7 ± 0.4 g/L was reached in microcultivation that was lower than when cadaverine transaminase was used. The elongation of the new pathway by 5AVA transamination by GABA/5AVA aminotransferase (GabT) and oxidation by succinate/glutarate semialdehyde dehydrogenase (GabD) allowed for glutarate production. Flux enforcement by the disruption of the l-glutamic acid dehydrogenase-encoding gene gdh rendered a single transaminase (GabT) in glutarate production via the new pathway responsible for nitrogen assimilation, which increased the glutarate titer to 7.7 ± 0.7 g/L, i.e., 40% higher than with two transaminases operating in glutarate biosynthesis. Flux enforcement was more effective with one coupling site, thus highlighting requirements regarding the modularity and stoichiometry of pathway-specific flux enforcement for microbial production.
Highlights
Plastics are primarily synthesized chemically from petroleum and natural gas
Flux enforcement by the disruption of the l-glutamic acid dehydrogenase-encoding gene gdh rendered a single transaminase (GabT) in glutarate production via the new pathway responsible for nitrogen assimilation, which increased the glutarate titer to 7.7 ± 0.7 g/L, i.e., 40% higher than with two transaminases operating in glutarate biosynthesis
The operation of the reactions of PatA and/or GABA/5AVA aminotransferase (GabT) in the glutarate production pathway obviates the need to synthesize l-glutamic acid from 2-oxoglutarate and ammonium by NADPH-dependent l-glutamic acid dehydrogenase, which is encoded by gdh
Summary
Plastics are primarily synthesized chemically from petroleum and natural gas. the annual market volume of bioplastics is predicted to increase from 2.11 million tons in 2019 to 2.43 million tons in 2024 [1]. Polyamides can be produced via two routes: either by the condensation of dicarboxylic acids with diamines or by the anionic ring-opening polymerization of lactams, which can be formed from ω-amino acids via cyclization [4]. Examples of these main building blocks range from succinate to sebacate for Catalysts 2020, 10, 1065; doi:10.3390/catal10091065 www.mdpi.com/journal/catalysts. All three precursors can be synthesized from the amino acid l-lysine by a series of oxidation, decarboxylation, and deamination reactions; fermentative routes for their production have been established
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