Regulation in functional metabolic pathways improves heat tolerance and biomass accumulation of Scenedesmus quadricauda cells

To improve heat tolerance and biomass yield of microalgae cells cultivated with flue gas in power plants in South China in summer, Scenedesmus quadricauda cells were cultivated at various temperatures to regulate functional metabolic pathways. The microalgae biomass production was 26 % higher at 35°C than at 25°C. The expression of photosynthesis-related proteins was up-regulated by 14.3 %, enhancing electron transfer efficiency and oxygen release rate at photosynthetic carbon fixation. Furthermore, microalgal cells absorbed more sulfur to enhance sulfur metabolism. The extracellular polymeric substances (EPS) content increased by 2.71-fold, improving the survival activity under high-temperature stress. The up-regulation of lysosomes and hydrogenases promoted the cellular removal of metabolic wastes and damaged organelles and improved the antioxidant defense capacity. Moreover, the microalgal cells maintained normal growth at 40°C through a self-regulatory mechanism. In contrast, the photosynthetic carbon fixation of microalgae cells was strongly inhibited at 42°C. This study revealed the adaptive mechanism of cellular carbon fixation in microalgae at high temperatures, which improved the high-temperature tolerance and biomass production of microalgae.