Enhanced Lipid Accumulation through a Regulated Metabolic Pathway of Phosphorus Luxury Uptake in the Microalga Chlorella vulgaris under Nitrogen Starvation and Phosphorus Repletion

摘要

To determine the underlying causes of increased lipid productivity in Chlorella vulgaris, cells were grown in nitrogen-starved phosphorus-replete (N-P+) conditions, and oxidative phosphorylation pathways, luxury phosphorus uptake, photosynthetic characteristics, and lipid productivity were investigated. A maximum lipid productivity of 82.0 mg L-1 day(-1) was obtained under N-P+ conditions, which was 4.6-fold and 1.5fold higher than that obtained under nitrogen and phosphorus-replete and N-Plim conditions, respectively. Genes involved in oxidative phosphorylation, including ATP synthase (fold change = 38.74), ATP phosphohydrolase (fold change = 18.19), inorganic pyrophosphatase (fold change = 25.94), and NADH dehydrogenase, were primarily upregulated in N-P+ conditions. The ATP and total ATPase contents in cells were greater under N-P+ conditions than under control conditions, which suggests there may be a greater energy supply for lipid biosynthesis under N-P+ conditions. P-31 NMR spectra results indicate that phosphorus was luxuriously assimilated by cells under N-P+ conditions and was mainly stored as pyrophosphate, polyphosphate, orthophosphate, and monoesters. The maximum quantum efficiency and relative electron transport rate of C. vulgaris cultivated under N-P+ conditions were 0.55 and 23, respectively, which were greater than under nitrogen-starved phosphorus-limited (N-Plim) conditions. Nitrogen starvation and phosphorus repletion is undoubtedly an optimal strategy for lipid accumulation.