The utilization of photophosphorylation uncoupler to improve lipid production of Chlorella, a case study using transcriptome and functional gene expression analysis to reveal its mechanism

Abstract

Uncoupling of photophosphorylation appears to have positive effect on lipid production of microalgae, however, underlying mechanisms involved in the effect are still unresolved. In this study, an uncoupler of photophosphorylation, carbonyl cyanide m-chlorophenyl hydrazone (CCCP), was used for the promotion of microalgal lipid accumulation. The results indicated that addition of CCCP was able to enhance the lipid productions of all tested species of Chlorella, especially when cultivated under mixotrophic condition. Based on the transcriptome and functional gene expression analyses, the functional genes involving in photosynthetic electron transport (PET), fatty acids synthesis, tricarboxylic acid (TCA) cycle, glycolysis and pentose phosphate (PP) pathway were found to be up-regulated while the genes participating in photosystem II, ATP synthesis during photosynthesis and calvin cycle were to be down-regulated by the presence of CCCP. According to these observations, the mechanism of CCCP to the promotion of lipid synthesis probably through channeling the NAD(P)H metabolic fluxes from carbon fixation towards fatty acid biosynthesis and lipid production, which was accomplished by (1) down-regulation of ribulose-1,5-bisphosphate carboxylase/oxygenase genes that involving in CO2 fixation via calvin cycle to reduce the NADPH consumption; (2) up-regulation of genes involved in TCA cycle and PP pathway to produce more NAD(P)H. The results of this study provide a new method to promote microalgal lipid production.