Low-molecular-mass organic acid and lipid responses of Isochrysis galbana Parke to high temperature stress during the entire growth stage

Abstract Isochrysis galbana is an important food source in aquaculture especially in the rearing of bivalve mollusks and usually cultured in summer, when water temperatures in breeding pools may reach 35 °C. However, the impact of high temperature stress on the growth and metabolism of I . galbana is poorly understood. In this study, the changes of total superoxide dismutase (T-SOD) activity, organic acid, and lipid levels were analyzed at different growth stages when I . galbana Parke was cultured under normal temperature (20 °C) and extreme high temperature (35 °C), respectively. The result showed that T-SOD activity reached the highest level at exponential phase at both temperatures but exhibited lower level during growth at 35 °C. The lower content of citric acid and α-ketoglutaric acid during late stationary phase indicated that tricarboxylic acid (TCA) cycle, amino acid metabolism, and the synthesis of fatty acids may severely be damaged under high temperature stress. The upregulation of monogalactosyldiacylglycerol (MGDG), diacylglycerylcarboxyhydroxymethylcholine (DGCC), diacylglyceryl- N , N , N -trimethylhomoserine (DGTS), triacylglycerol (TAG), and lyso-lipids was observed from adaptation phase to early stationary phase. But downregulation of glyceroglycolipids (MGDG, DGDG, and SQDG), DGCC, and DGTS were found between early stationary phase and late stationary phase at high temperature. Besides, the level of DHA decreased under high temperature stress, revealing that the nutritional value of I . galbana Parke had been reduced. This is the first report addressing metabolic responses of I . galbana Parke to high temperature stress combining T-SOD activity, organic acid, and lipid analysis, and the results demonstrated that the extreme high temperature (35 °C) will not only suppress the activity of T-SOD and the formation of organic acids in the TCA cycle and photorespiration, but also influence the lipid metabolism in I . galbana Parke. This study provided a useful reference value for the cultivation of I . galbana under high temperature condition.