Acclimation of photosynthesis and lipids biosynthesis to prolonged nitrogen and phosphorus limitation in Nannochloropsis gaditana

Microalgae represent a potential sustainable source of molecules and materials and the improvement of the knowledge of their metabolic regulation is essential to maximize their potential. Nutrients deprivation stimulates the accumulation of reserve lipids, triacylglycerols but also inhibits photosynthesis with a negative impact on biomass production and therefore overall productivity. In this work, the seawater microalga Nannochloropsis gaditana was cultivated long term in a semi-continuous system where the concentrations of nitrogen or phosphorus were limiting but still sufficient to sustain growth indefinitely, to highlight the response to a long-term nutrient limitation and distinguishing it from the one to acute short-term stress. N. gaditana cells can acclimate to chronic nutrients limitation maintaining photosynthetic activity while also accumulating lipids. Both nitrogen and phosphorus limitation induced an increase of triacylglycerols content, although not by the induction of the synthesis of fatty acids but rather by modulating the fluxes of reduced carbon molecules toward lipid biosynthesis. Photosynthetic activity was maintained under P limitation while this was strongly affected by nitrogen depletion, where proteins of photosynthetic apparatus were largely reduced in content but still maintained their functionality and were able to achieve half of the biomass productivity with 30% of the nitrogen supply.

Automated summary

This study found that the microalgae Nannochloropsis gaditana can acclimate to chronic nitrogen or phosphorus limitation by accumulating lipids without inducing fatty acid synthesis but by modulating carbon flux towards lipid biosynthesis, maintaining photosynthetic activity. Moreover, photosynthetic activity was maintained under phosphorus limitation but was strongly affected by nitrogen depletion.