Enhanced production of C₅₀ carotenoid bacterioruberin by metabolically engineered Corynebacterium glutamicum

Bacterioruberin is a red-pigmented C₅₀ carotenoid commonly found in halophilic archaea, known for its strong antioxidant properties. In this study, we demonstrate the complete biosynthesis of bacterioruberin in metabolically engineered Corynebacterium glutamicum overproducing lycopene. To investigate the function of the encoded enzymes, we genetically modified C. glutamicum to produce lycopene and constructed recombinant C. glutamicum strains expressing bacterioruberin biosynthetic genes. The carotenoids produced by the recombinant strains were then analyzed. The pathway comprising the bifunctional lycopene elongase and 1,2-hydratase (lyeJ), carotenoid 3,4-desaturase (crtD), and C₅₀ carotenoid 2'',3''-hydratase (cruF) from "Haloferax marinum" was introduced into the C. glutamicum ΔcrtRYEb strain. The expression of each gene allowed for the identification of bacterioruberin, its known precursors, and previously unidentified precursors. In fed-batch fermentation, a carotenoid titer of 9.74 mg/L with a yield of 0.29 mg/g DCW and a productivity of 0.30 mg/L/h, was achieved. This study is the first to demonstrate that C. glutamicum can accumulate the non-native bacterioruberin instead of its native cyclic C₅₀ carotenoid, decaprenoxanthin.