Blue LED-assisted bioreactor cultivation enhances carotenoid accumulation in Rhodotorula mucilaginosa LB-01.

Microbial production of carotenoids provides a sustainable alternative to plant-derived sources. In this study, a yeast strain, Rhodotorula mucilaginosa LB-01, was isolated and its carotenoid biosynthetic potential was evaluated. Medium optimization (10 g/L glucose and 3 g/L yeast extract) improved relative carotenoid accumulation, reaching 10.13 Abs/g dry biomass. The influence of light quality was subsequently assessed, showing that blue LED illumination was associated with higher relative carotenoid accumulation (12.4 Abs/g) compared with red, orange, white, and green light conditions. Cultivation in a stirred-tank bioreactor (2.5 L working volume) under blue LED illumination resulted in further increases in carotenoid accumulation, reaching 16 Abs/g and 311 µg/g dry biomass, corresponding to an approximately 20% increase compared with control conditions operated without direct light exposure. Purification and quantification of individual pigments identified torularhodin (173 µg/g), torulene (71 µg/g), and β-carotene (67 µg/g), all present at higher levels than in the control. Overall, these results indicate that R. mucilaginosa LB-01, combined with controlled LED illumination, represents a promising microbial system for carotenoid accumulation. KEY POINTS: • Rhodotorula mucilaginosa LB-01 was identified as a carotenoid-producing yeast. • Blue LED illumination yielded the highest relative carotenoid accumulation (12.4 Abs/g). • Blue LED bioreactor cultivation increased accumulation to 16 Abs/g dry biomass (+ 20%).