Qualitative analysis of algal secretions with multiple mass spectrometric platforms

Abstract

Lipid secretions from algae pose a great opportunity for engineering biofueler feedstocks. The lipid exudates could be interesting from a process engineering perspective because lipids could be collected directly from the medium without harvesting and disrupting cells. We here report on the extracellular secretions of algal metabolites from the strain UTEX 2341 (Chlorella minutissima) into the culture medium. No detailed analysis of these lipid secretions has been performed to date. Using multiple mass spectrometric platforms, we observed around 1000 compounds and were able to annotate 50 lipids by means of liquid chromatography coupled to accurate mass quadrupole time-of-flight mass spectrometry (LC-QTOF), direct infusion with positive and negative electrospray ion trap mass spectrometry and gas chromatography coupled to mass spectrometry (GC-MS). These compounds were annotated by tandem mass spectral (MS/MS) database matching and retention time range filtering. We observed a series of triacylglycerols (TG), sulfoquinovosyldiacylglycerols (SQDG), phosphatidylinositols and phosphatidylglycerols, as well as betaine lipids diacylglyceryl-N,N,N-trimethylhomoserines (DGTS).