Disturbance of respiration-improved lipid biosynthesis in Auxenochlorella pyrenoidosa (Chlorellaceae, Chlorophyta) under nitrogen limitation

Understanding the related mechanisms between aerobic respiration and lipid biosynthesis may promote microalgal-biofuel industries through metabolic engineering. However, little is known about how aerobic respiration affects lipid biosynthesis in microalgae. Here, the changes in biochemistry and molecular biology were analysed in Auxenochlorella pyrenoidosa throughout nitrogen limitation (–N) and nitrogen resupply (+N) phases. Respiratory inhibitors were used to identify the roles of respiratory complexes in lipid biosynthesis. We found that during –N phase the growth profiles, and the amount and productivity of chlorophyll a, carbohydrates and proteins decreased, while the content and productivity of lipids increased. In addition, the lower unsaturation (DU ≤ 96.41 ± 0.38) showed that lipid accumulation under nitrogen limitation in A. pyrenoidosa was qualified for biodiesel production. Either relationships or significant correlations were found between lipid contents, reactive oxygen species (ROS), respiration rates, respiratory complexes activities and key gene expression in treatment groups. Moreover, the trends in the activities of complexes I and III, lipid contents and ROS production in +N phase were different from those in –N phase. Finally, the respiratory inhibitors increased the levels of total ROS and lipids in A. pyrenoidosa. These results suggested that nitrogen limitation may inhibit redox centers of complexes I and III in respiratory chains through mitochondria and nucleus, thus regulating intracellular ROS and lipid accumulation.