Scale up production of astaxanthin by using recombinant yeast-Kluveromyces marxianus

Astaxanthin (AXT) is a dark-red ketocarotenoid from the xanthophyll group, renowned for its anti-inflammatory, antioxidant, and anti-proliferative properties, which is widely applied in animal feed, food, cosmeceuticals, and pharmaceuticals. Recently, the growing recognition of AXT’s numerous health benefits has significantly boosted both industrial and research interest in this remarkable compound. Synthetic biology represents a cost-effective strategy for the targeted production of specific optical isomers of natural compounds. This study explores the scale-up production of free-form 3S, 3'S astaxanthin (Asta-S) using recombinant probiotic yeast Kluyveromyces marxianus . Among various carbon sources tested, glucose was identified as the most practical substrate due to its cost-effectiveness, although galactose induced higher astaxanthin yields. Increasing glucose concentration from 20 to 80 g/L enhanced biomass but slightly reduced astaxanthin content in flask cultures. In 5 L fermenter trials, biomass growth increased with higher initial glucose levels, with the highest total astaxanthin yield of 41.06 mg/L achieved at 80 g/L glucose. To overcome carbon depletion and enhance productivity, a glucose fed-batch strategy was applied, resulting in the improved astaxanthin yield of 51.22 mg/L with a productivity of 0.711 mg/L/hr. The process was further scaled to a 30 L in-situ fermenter, where pressurized cultivation at 1 atm enhanced dissolved oxygen availability, resulting in higher astaxanthin content (4.38 mg/g) and improved biomass compared to atmospheric pressure fermentation. These results confirm the potential of recombinant K. marxianus 929 Asta strain D56 as a viable host for industrial astaxanthin production, particularly when leveraging fed-batch strategies and controlled pressure fermentation for scalability.