Modulation of PUFA and PUA production in coastal diatoms by varying light and phosphate availability

As climate change intensifies and resource sustainability becomes crucial, diatoms represent a promising source of bioactive compounds. Among them, polyunsaturated fatty acids (PUFA) stand out for their essential biological roles and high value in fields such as medicine, aquaculture and bioenergy. However, in several diatom species, PUFA productivity can be reduced due to their enzymatic conversion into polyunsaturated aldehydes (PUA), compromising their biotechnological potential. To evaluate the true potential of PUA-producing diatoms as PUFA sources, we introduced a transformation ratio metric that estimates the proportion of PUFA availability after PUA production. This metric was applied to three coastal diatoms ( Thalassiosira minima , Skeletonema pseudocostatum , and Cyclotella cryptica ) cultured under different phosphate availability and light conditions. A selection framework identified T. minima as unsuitable due to high PUA production relative to PUFA levels. S. pseudocostatum and C. cryptica were further analyzed, showing different optimal culture conditions. In S. pseudocostatum , high phosphate and cool white light conditions reduced PUA production, while warm light and continuous photoperiods increased cell stress and PUA production, raising the transformation ratio to the maximum detected (21.93 ± 5.10 %). In contrast, C. cryptica showed stable PUA production across treatments and enhanced PUFA availability under low phosphate and cool light. Under these conditions, PUFA concentration reached 1181.81 ± 209.11 fmol cell −1 , the highest among all species and condition tested. This study provides a biotechnological screening criterion for PUA-producing diatom optimizing culture conditions. • The content and quality of valuable PUFA in three PUA-producing diatoms are highly influenced by light and phosphate conditions. • A new transformation ratio from PUFA to PUA (TR) is introduced to assess the biotechnological potential of these three diatoms. • Environmental stress increased PUA production, TR but also compromised cell viability. • Crucially, PUA production did not significantly deplete PUFA resources in these three species.