Process of a Photobacterial Cascade Reaction for Biobased Adipic Acid

Adipic acid, a crucial monomer in polymer synthesis, plays a significant role in the production of food packaging materials. In the context of the “Dual Carbon” strategy, the advancement of biobased adipic acid is of critical importance. Here, we have developed an innovative photobacterial cascade reaction system for adipic acid synthesis, which represents a groundbreaking approach in production methodology. The pathway with l-lysine as the precursor is a potential pathway for adipic acid synthesis, but it is subject to low catalytic activity or unknown enzymes in some reactions. In this study, the biosynthesis pathway of l-2-aminoadipate, an intermediate metabolite of adipic acid synthesis with l-lysine as the precursor, was constructed in Corynebacterium glutamicum. It was determined that the coexpression of lysine 6-dehydrogenase from Geobillus sp. 12AMOR1 and aminoadipate semialdehyde dehydrogenase from Pseudomonas fulva 12-X was more beneficial to the synthesis of l-2-aminoadipate. Regulation of the expression of the above enzymes and overexpression of key genes in the precursor lysine synthesis pathway increased l-2-aminoadipate production to 1.02 g/L, which was 6.4 times higher than that of the parental strain. Subsequently, the synthesis of l-2-aminoadipate to adipic acid was realized by photocatalytic conversion instead of the conversion by unknown enzymes. A photocatalyst could complete the oxidation process of deamination by using electron–hole pairs. By optimizing the photocatalytic materials, the treated rape pollen (TRP) was determined as the better photocatalyst. TRP was added as a catalyst in the fermentation system of producing l-2-aminoadipate by C. glutamicum, and the light system was introduced to achieve the photocatalytic conversion of l-2-aminoadipate to adipic acid. 235 mg/L adipic acid could be produced after 48 h of fermentation. A method for producing adipic acid by microbial fermentation coupled with photocatalysis was successfully developed, which broadens the routes for the synthesis of adipic acid. In addition, the photomicrobial cascade reactions could replace the catalytic processes of unknown enzymes, providing new ideas for the synthesis of other important chemicals.