Efficient fucoxanthin production by fed-batch photo-fermentation cultivation of genetically engineered...

The marine diatom Phaeodactylum tricornutum is considered a promising platform for commercial fucoxanthin production due to its naturally high fucoxanthin content. However, its industrial application remains limited by low biomass productivity and high production costs associated with conventional photoautotrophic cultivation. To address these challenges, metabolic engineering was employed to convert the obligate photoautotrophic strain into a glucose-utilizing strain capable of heterotrophic growth, thereby enabling high-density cultivation. In this study, the wild-type P. tricornutum Pt1 was genetically engineered, and the transformant Glut1-45 was identified as the superior strain based on its enhanced growth performance compared with other transformants. Subsequently, an efficient photo-fermentation process was developed through systematic optimization of cultivation conditions for Glut1-45. The results demonstrated that light supplementation, together with a mixed nitrogen source containing inorganic sodium nitrate and organic tryptone, markedly enhanced glucose utilization and cell growth. Moreover, Glut1-45 exhibited no significant growth inhibition at glucose concentrations below 10 g L^-1, whereas concentrations exceeding 20 g L^-1 significantly inhibited cell proliferation. By maintaining glucose concentrations below 5 g L^-1 during fed-batch photo-fermentation, high-cell-density cultivation and enhanced fucoxanthin production were successfully achieved. The maximum biomass concentration reached 10.05 g L^-1, while the maximum fucoxanthin content reached 14.87 mg g^-1 dry cell weight, yielding the highest fucoxanthin titer of 146.58 mg L^-1. These results demonstrate the potential of integrating metabolic engineering for glucose utilization with fed-batch photo-fermentation to achieve high-cell-density cultivation and enhanced volumetric fucoxanthin production, providing a feasible strategy for efficient P. tricornutum-based fucoxanthin biomanufacturing.