Intermittent light enhances pigment production in the diatom Phaeodactylum tricornutum : a combined physiological and transcriptomic approach

ABSTRACT Diatoms are ecologically important microorganisms that rely on dynamic pigment regulation for light use and photoprotection. These pigments also possess antioxidant, UV-protective, and anti-inflammatory properties, making them valuable for both ecological and biotechnological applications. While pigment biosynthesis in diatoms is well studied, the molecular responses to intermittent light environments remain poorly understood. Here, we investigated the adaptation of the model diatom Phaeodactylum tricornutum to simulated seasonal and intermittent light–dark (LD) cycles using a combination of physiological and transcriptomic analyses. We assessed growth, pigment content, photosynthetic performance, and elemental composition under different LD regimens (LD 24:0, LD 16:8, LD 12:12, LD 8:16, LD 4:2, LD 2:2, and LD 2:4). Our results showed that intermittent light stimulated growth and photosynthetic efficiency, with the highest pigment content observed under the LD 2:2 regimen. This regimen also increased the ratio of photosynthetic to photoprotective pigments and reduced diadinoxanthin de-epoxidation. Transcriptomic data revealed that moderate LD cycles (LD 2:2 and LD 12:12) upregulated genes involved in chlorophyll and carotenoid biosynthesis, as well as light-harvesting complex pathways. This study provides key insights into the molecular and physiological strategies diatoms employ to adapt to variable light environments and highlights their potential for improved pigment production in industrial and biotechnological applications. IMPORTANCE Diatoms are tiny algae that play a key role in Earth's ecosystems by absorbing carbon and producing oxygen. They also create valuable pigments with properties that can protect against environmental stress and may have uses in health, food, and industry. This study reveals how diatoms adapt to changing light conditions, which are common in natural waters. Researchers found that short intervals of light and darkness can boost diatom growth and increase pigment production, especially under very short light cycles. By exploring the genes and biochemical processes involved, the study offers new insight into how these microorganisms survive in dynamic environments. This knowledge could help improve the sustainable production of diatom-derived pigments for a range of practical applications, from food coloring to natural health products.