Molecular basis of autotrophic vs mixotrophic growth in Chlorella sorokiniana

Abstract

In this work, we investigated the molecular basis of autotrophic vs. mixotrophic growth of Chlorella sorokiniana, one of the most productive microalgae species with high potential to produce biofuels, food and high value compounds. To increase biomass accumulation, photosynthetic microalgae are commonly cultivated in mixotrophic conditions, adding reduced carbon sources to the growth media. In the case of C. sorokiniana, the presence of acetate enhanced biomass, proteins, lipids and starch productivity when compared to autotrophic conditions. Despite decreased chlorophyll content, photosynthetic properties were essentially unaffected while differential gene expression profile revealed transcriptional regulation of several genes mainly involved in control of carbon flux. Interestingly, acetate assimilation caused upregulation of phosphoenolpyruvate carboxylase enzyme, enabling potential recovery of carbon atoms 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 fine regulation of cell metabolism.

Chlorella vulgaris genome assembly and annotation reveals the molecular basis for metabolic acclimation to high light conditions

“…Notably, based on the KEGG Mapper tool, all enzymes required for a C4‐like carbon fixation pathway are present in the C. vulgaris 211/11P genome (Figure S6), with the key enzyme involved in carbon fixation in C4 compound phosphoenolpyruvate carboxylase (PPC), encoded by two genes g3928 and g4635, predicted in the cytosol and in the mitochondria, respectively. These two isoforms of PPC might have a role in oxaloacetate formation in the anaplerotic reactions, or for gluoconeogenesis or as alternative carbon fixation to RUBISCO, as previously suggested for C. sorokiniana (Cecchin et al ., ).…”

“…Proteins and starch content of the harvested biomass were analyzed as reported previously in Cecchin et al . ().…”

Systems biology approach identifies functional modules and regulatory hubs related to secondary metabolites accumulation after transition from autotrophic to heterotrophic growth condition in microalgae

“…To overcome the poor biomass accumulation, open ponds that mimic natural environments of the microalgae are alternative option for the most commercial microalgae [5]. These cultivation systems present relatively lower construction and operating costs and large ones can be constructed on nonagricultural lands [6]. Nevertheless, these cultivation systems have several disadvantages such as expensiveness in the harvesting step, continuous need to clean water; unfeasibility for the secondary metabolite production; and susceptibility to environmental conditions [6].…”

“…These cultivation systems present relatively lower construction and operating costs and large ones can be constructed on nonagricultural lands [6]. Nevertheless, these cultivation systems have several disadvantages such as expensiveness in the harvesting step, continuous need to clean water; unfeasibility for the secondary metabolite production; and susceptibility to environmental conditions [6]. To control environmental parameters during cultivation, closed photobioreactors have been designed [7].…”

Comparison of photoautotrophic and mixotrophic cultivation of microalgae Messastrum gracile (Chlorophyceae) in alternative culture media

“…However, some microalgae species have also the peculiar capability to growing in mixotrophic mode, where the autotrophic metabolism is integrated with heterotrophic metabolism that oxidizes the reduced carbon source available in the culture medium. However, in case of some microalgae, the photosynthetic efficiency may be reduced in mixotrophic cultivation (Cecchin et al, 2018).…”