PRJNA416862
DIFFERENTIAL GENE EXPRESSION ANALYSIS OF CHLORELLA SOROKINIANA CULTIVATED IN AUTOTROPHIC VS. MIXOTROPHIC CONDITIONS
Chlorella species are among the most interesting microalgae for biomass and biofuel production because of the high productivity, high lipid content and resistance to high light conditions. Moreover, several Chlorella sp. can be cultivated in mixotrophy, adding a reduced carbon substrate as a source of energy in addition to the photosynthetic process. In this work, we investigated the molecular basis of autotrophic vs. mixotrophic growth of Chlorella sorokiniana UTEX1230 strain. In mixotrophic conditions we observed an enhanced biomass, proteins, lipids and starch productivity when compared to autotrophic conditions. Despite decreased chlorophyll and chlorophyll binding protein accumulation, photosynthetic properties were essentially unaffected in C. sorokiniana by acetate addition. Differential gene expression profile in autotrophy as compared to mixotrophy was then investigated by the mean of RNAseq and transcriptome reconstruction. In mixotrophy we observed down-regulation of genes involved in light harvesting complex, among which the subunit PSBS, putatively involved in Non-Photochemical Quenching of the light absorbed. Downregulation of glycolytic enzymes and upregulation of genes involved in amino acids biosynthesis were linked with increased starch and proteins accumulation in mixotrophy. Acetate assimilation caused upregulation of photorespiratory enzymes producing glyoxylate to be used for acetate derived acetyl-CoA condensation into malate. Moreover, in mixotrophy we observed the upregulation of phosphoenolpyruvate carboxylase enzyme, enabling potential recovery of carbon lost by acetate oxidation. The obtained results allowed to associate the increased productivity observed in mixotrophy in C. sorokiniana with a different gene regulation leading to a change of metabolic pathways.