HR MAS NMR spectroscopy of marine microalgae

Abstract

Microalgae provide organic carbon through primary production and although most species are harmless, a few are toxic or otherwise damaging to animal and human life. Microalgae are used to produce biodiesel or feed in aquaculture or health food for human consumption, and species determination and knowledge of nutritional value is therefore needed. Common methods used in studies of microalgae provide only partial information, and sample preparation is often tedious and requires extraction with organic solvents. Application of highresolution magic angle spinning (HR MAS) 1 H NMR spectroscopy gave wellresolved spectra directly from whole cells of several different marine microalgae, and comparison with spectra from extraction samples showed that both analyses provide to a large extent the same information on metabolite composition. The application of HR MAS NMR leads to increased signal resolution in semi-solid samples such as whole cells and organs, and this has made NMR a very interesting analytical tool to biologists, e.g., for metabolic profiling of microalgae. Polyunsaturated fatty acids (PUFAs) eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids were seen in a 1 H NMR spectrum of lipophilic extract of the diatom Thalassiosira pseudonana, while in a spectrum of hydrophilic extract we assigned signals to amino acids glutamine (Gln) and glutamic acid (Glu), carbohydrate, and ATP. Furthermore, HR MAS 1 H NMR spectroscopy in combination with the multivariate statistical principal component analysis (PCA) was used to separate groups of marine microalgae, and our results indicate that it is possible also to classify (or separate) species within the different groups. The PCA outcome was influenced by cellular content of various osmolytes, which indicates that the NMR spectra reflect signals from nuclei in liquid cellular compartments. This can be used to study cellular dynamics and transport of metabolites between different cellular locations, but also indicates that nuclei in other cellular locations are partly suppressed in the NMR analysis. Since the use of HR MAS 1 H NMR spectroscopy is relatively new in biological studies the methodological possibilities and restrains should be investigated closely, but our results support the use of NMR spectroscopy on whole-cell samples of microalgae.