OPTIMIZATION OF CONDITIONS FOR HETEROTROPHIC-LIGHT COUPLING HIGH-DENSITY CULTIVATION OF POTERIOOCHROMONAS MALHAMENSIS FOR FUCOXANTHIN PRODUCTION

Fucoxanthin, a carotenoid pigment primarily derived from brown macroalgae and marine microalgae, stands out as one of the most abundant carotenoid, constituting over 10% of the total natural carotenoids production. Its distinctive molecular structure renders it applicable in various industries, including health care, medicine, cosmetic, and others. Previous studies have reported that Poterioochromonas malhamensis can accumulate fucoxanthin through a photoinduction strategy, achieving a relatively high level of 25.6 mg/L under inorganic nitrogen source culture conditions. Despite the promising efficiency displayed by P. malhamensis in fucoxanthin production efficiency, commercial fucoxanthin production remains a formidable challenge. Therefore, enhancing the overall performance of fucoxanthin production from P. malhamensis through process engineering strategies is crucial. In this study, in order to further improve the comprehensive performance of fucoxanthin production by P. malhamensis, the fermentation conditions including carbon-to-nitrogen (C/N) ratio of the P. malhamensis fermentation medium, and the adding concentration of vitamins into fermentation medium were firstly investigated. The results showed that a C/N ratio of 24, along with the additions of 3.75 mg/L of vitamin B₁ and 1.25 mg/L of vitamin B₁₂, fostered efficiently fucoxanthin synthesis in P. malhamensis cells. Additionally, a comparative study of P. malhamensis growth, maximum photosynthetic efficiency, and fucoxanthin accumulation under different light and dark culture modes was conducted. The results showed a significant enhancement in intracellular fucoxanthin content with continuous light induction throughout the entire culture process, from seed culture to fermentation in the stirred bioreactor. Through systematic optimization of the culture process, intracellular fucoxanthin content and yield reached higher levels of 1.79 mg/g and 33.6 mg/L, respectively. These values were 33.6% and 31.2% higher than those achieved in the non-optimized process. This study effectively enhanced the fucoxanthin accumulation capability of P. malhamensis through fermentation optimization and process control strategies, providing a preliminary foundation for further large-scale process amplification, and serving as a reference for other microalgae in high-efficiency fucoxanthin production.