Content, Ratio and Productivity of Amphidinols in Wild-Type and Mutagenized Strains of Amphidinium carterae at Different Growth Stages

As agriculture faces increasing pressure to reduce pesticide residues and heavy metal accumulation in soils, marine microalgae are emerging as sustainable sources of biopesticides. Among them, <i>Amphidinium carterae</i> produces amphidinols (AMs), polyketide metabolites with strong antifungal activity against crop pathogens. Currently, large-scale AM production remains constrained by a limited understanding of AM biosynthesis across different <i>A. carterae</i> growth phases and by the lack of high-performing industrial strains. In this study, AM production dynamics were investigated in one wild-type (WT) and five mutagenized <i>A. carterae</i> strains. The production of bioactive AM18 and its sulfated inactive form AM19 was monitored through exponential, linear, and early stationary growth phases. The maximum AM productivity occurred between the linear and early stationary phase, with the average values of 5.58 ± 0.4 and 3.58 ± 0.2 µg/mL/day for AM18 and AM19, respectively. The AM18/AM19 ratio consistently decreased with the culture age, indicating that earlier harvesting favors higher proportions of bioactive AMs. UV mutagenesis increased the AM18 cell content by more than twofold and the growth rate by up to 20% in certain mutagenized strains compared to the WT strain, but did not enhance the volumetric AM productivity. Overall, these results identify optimal AM harvesting windows and clarify the potential benefits of mutagenesis strain improvement for industrial AM production improvement.