Improved lipid productivity in Nannochloropsis gaditana in nitrogen replete conditions by selection of pale green mutants

Nannochloropsis gaditana is a photosynthetic unicellular microalga considered one of the most interesting marine algae to produce biofuels and food additive due to its rapid growth rate and high lipids accumulation. Although microalgae are attractive platforms for solar energy bioconversion, the overall efficiency of photosynthesis is reduced due to the steep light gradient in photobioreactors. In this work a biotechnological approach was directed for the isolation of strains with a reduction chlorophyll content per cell, to improve light penetration in the photobioreactor, combined with increased lipids productivity. Accordingly, one mutant, called e8, was selected: this mutant is characterized by a 30% reduction of chlorophyll content per cell and an almost 80% increase of lipid productivity compared to WT. Reduced chlorophyll content per cell and more homogenous irradiance in photobioreactor in the e8 mutant is proposed to be at the base for the increased lipid productivity observed, being lipid biosynthesis regulated by the light availability in several microalgae species, including Nannochloropsis gaditana. The whole genome sequencing of the e8 mutant strain suggests possible genes responsible of the observed phenotypes, identifying putative target for future complementation and biotechnological application. Mutation in dgd1 synthase gene is a possible candidate to explain the phenotype observed being involved in the biosynthesis of DGDG, one of the major lipids found in the thylakoid membrane.