Cold stress treatment enhances production of metabolites and biodiesel feedstock in Porphyridium cruentum via adjustment of cell membrane fluidity

Highlights: • Removal of a 5-day cold stress at 0 °C increased biomass of Porphyridium cruentum. • Cultivation of P. cruentum for 5 days at 0 °C remarkably increased PUFA content. • Zeaxanthin of P. cruentum was markedly accumulated after the 5-day 0 °C treatment. • P. cruentum responded to the cold stress by changing its cell membrane fluidity. • An arm-raising/screw-bolt fastening hypothesis explained the cold stress response. Porphyridium cruentum, a cell-wall-free marine Rhodophyta microalga was cultured under a 5-day cold stress at 0 °C and 15 °C, after reaching the late logarithmic growth phase. Compared with the control at 25 °C, the cold stress treatment significantly (p < 0.05) increased the microalgal biomass (1.21-fold); the amounts of total polyunsaturated fatty acids (1.22-fold); individual fatty acids including linoleic acid (1.50-fold) and eicosatrienoic acid (1.85-fold), and a major carotenoid zeaxanthin (1.53-fold). Furthermore, production of biodiesel feedstock including total C₁₆ + C₁₈ fatty acids was significantly enhanced (p < 0.05) by 1.18-fold after the cold stress treatment. Principal component analysis further indicated that the biosynthetic pathways of fatty acids and carotenoids in this microalga were correlated with the cold stress treatment. These results suggested that P. cruentum had adjusted its cellular membrane fluidity via an 'arm-raising and screw-bolt fastening' mechanism mediated by the synergistic roles of cis-unsaturated fatty acids and carotenoids. The insight obtained from the responses to cold stress in P. cruentum could be a novel technological approach to enhance the production of microalgal metabolites and biodiesel feedstock.