Mass spectrometry-based metabolomics of value-added biochemicals from Ettlia oleoabundans

Microalgae are promising feedstocks for biofuels and other value-added biochemicals. Ettlia oleoabundans, a non-model green microalga, produces increased levels of key precursors for lipid-based biofuels under nutrient stress conditions. Here, we introduce a method for analysis of hydrophobic metabolites in E. oleoabundans and apply this method to microalgae grown under different nutrient conditions. We combined targeted analysis using gas chromatography/tandem mass spectrometry (GC–MS/MS) with targeted and untargeted metabolomics using liquid chromatography-quadrupole-time-of-flight mass spectrometry (LC-Q-ToF MS). Our method allows simultaneous detection of compounds from major lipid families, and other value-added biochemicals using less biomass, hence allowing analysis of larger number of samples to be processed simultaneously. In this study, we showed that 202 metabolites were enhanced or depleted under nutrient stress and annotated 163 of these species. A complex regulation of different classes of metabolites under nutrient stress was observed. Overall, triacylglycerols and sulfoquinovosyldiacylglycerols were accumulated, chlorophylls were depleted, and diacylglycerols were differentially regulated at the molecular level when grown under limited nutrient conditions. The method that we developed will serve as a template for targeted and untargeted metabolomics in E. oleoabundans and other non-model microalgae to understand biochemical regulations under different experimental conditions.