Evaluating differences in growth, photosynthetic efficiency, and transcriptome of Asterarcys sp. SCS-1881 under autotrophic, mixotrophic, and heterotrophic culturing conditions

Abstract

Autotrophic microalgae can assimilate organic carbon sources for the growth of heterotrophy and mixotrophy. In particular, the physiological and biochemical response of different microalgae species on autotrophy, heterotrophy, and mixotrophy are quite different. The aim of the present study was to determine differences in growth, biochemical composition, photosynthetic characteristics, and metabolic pathway under autotrophic, heterotrophic and mixotrophic culture conditions in an oleaginous microalga, Asterarcys sp. SCS-1881. The results showed that Asterarcys sp. can use glucose for mixotrophic growth, but cannot under strict heterotrophic growth. Mixotrophic cultures can significantly increase the biomass concentration and cell count of Asterarcys sp. The microalga accumulated more protein under mixotrophic conditions, but more carbohydrates and total lipids under autotrophic conditions. The microalga under mixotrophic culture conditions showed significantly reduced pigment content, PSII activity, and photoprotective ability, but increased the activity of PSI when compared to those under autotrophic conditions. Under mixotrophic conditions, Asterarcys sp. also showed enhanced glycolysis, photosynthetic carbon fixation, and pentose phosphate pathway and thus more ATP, carbon skeleton structure, and NADPH. Additionally, the biosynthesis of triacylglycerol, carbohydrates, and pigments was reduced under mixotrophic conditions and the core protein complexes of PSI and PSII were attenuated. Similarly, photosynthetic electron transport and many other pathways related to protein synthesis were enhanced under mixotrophic conditions when compared to the microalga cultured under autotrophic conditions. These biochemical changes may work to co-operatively ensure a more efficient supply of energy and carbon skeleton for rapid growth of the microalga under mixotrophic conditions when compared to those raised under autotrophic conditions.