Transcriptomic analysis reveals the mechanism on the response of Chlorococcum sp. GD to glucose concentration in mixotrophic cultivation

In this study, the performance of Chlorococcum sp. GD in synthetic medium with different glucose concentrations (ranging from 1 to10 g/L) was investigated. Moreover, transcriptome sequencing was conducted to clarify the response of the microalga to glucose concentrations. High concentration of glucose (6-10 g/L) not only did not provide a higher yield of biomass but also inhibited photosynthesis. Transcriptomic analysis revealed that the glucose metabolism mainly depended on the glycolysis and the pentose phosphate pathway (PPP) as the microalga was cultivated with 10 g/L glucose. Meanwhile the tricarboxylic acid (TCA) cycle, oxidative phosphorylation and photosynthesis were significantly inhibited. The significant change on carbon metabolic flux caused by the increase in glucose concentration affected the synthesis of reducing power and ATP, which ultimately influenced the growth of the microalga. Appropriate supplement of organic carbon not only enhances the biomass accumulation but also increases the utilization efficiency of organic carbon.