A sequential and modular platform for red algal polysaccharide saccharification and De Novo microbial bilirubin biosynthesis

초록

Marine biomass represents a promising renewable feedstock for the sustainable production of high value bioactive compounds. In this study, integrated sequential saccharification and fermentation bioprocess was developed for the biosynthesis of bilirubin (BR) from red algal polysaccharides. To maximize the valorization of red algae, an optimized enzyme cocktail was employed, efficiently releasing D-galactose as the primary fermentable carbon source. To enhance BR production, Corynebacterium glutamicum was metabolically engineered through pathway level flux control. To increase the availability of the precursor biliverdin (BV), metabolic competition in the aspartate pathway was attenuated, while NADPH regeneration was reinforced via the pentose phosphate pathway. Crucially, pathway balancing was implemented to synchronize galactose assimilation with the BR biosynthetic flux. The final engineered strain produced 23.97 mg/L of BR in 1 L batch fermentation using galactose, achieving a yield of 0.60 mg/g BR/galactose. Functional validation through antioxidant assays confirmed that the microbially synthesized BR exhibited radical scavenging activity comparable to commercial standards. This sequential saccharification fermentation strategy demonstrates the feasibility of transforming low cost marine-derived polysaccharides into high value biopharmaceuticals through strategic metabolic modulation, providing a robust and economically viable platform for sustainable biomanufacturing.

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