Enhanced Production of Bioactive Polyunsaturated Fatty Acids and Pigments in Rhodosorus marinus: Optimization of Thermal and Photic Stress Conditions

The marine unicellular red alga <i>Rhodosorus marinus</i> is a promising source of the valuable phycobiliprotein phycoerythrin and essential omega-3 polyunsaturated fatty acids (PUFAs), yet the environmental triggers for their optimal co-production remain to be fully elucidated. This study was conducted to investigate the effects of thermal and photic stress in terms of maximizing the yield of these high-value bioactive compounds. <i>R. marinus</i> was cultivated under a range of temperatures (18-24 °C) and light intensities (100-335 µmol photons m^-2 s^-1) to assess its physiological and biochemical responses, particularly focusing on lipid accumulation. This study investigates the effects of thermal (18-24 °C) and photic (100-335 µmol photons m^-2 s^-1) stress on the concurrent production of the valuable phycobiliprotein, phycoerythrin (PE), and essential omega-3 polyunsaturated fatty acids (PUFAs) in the marine red microalga <i>Rhodosorus marinus</i>. Fatty acid profiles were quantified using gas chromatography (GC), while pigment content was assessed via spectrophotometry. Statistical analyses, including one-way ANOVA and Tukey's post hoc test, were employed to determine the significance of environmental effects. Our results demonstrate that a mild hypothermic condition of 18 °C significantly enhanced the production of eicosapentaenoic acid (EPA) compared to higher temperatures. Conversely, cell density was maximized at 22 °C. Under the 18 °C thermal regime, lower light intensities (100-185 µmol photons m^-2 s^-1) promoted a superior synthesis of both bioactive lipids and pigments. In conclusion, the strategic application of mild hypothermia combined with moderate light intensity is an effective approach to substantially boost the metabolic yield of high-value compounds in <i>R. marinus</i>, highlighting its potential as a sustainable source for nutraceutical and pharmaceutical applications.