Profiling whole microalgal cells by high-resolution magic angle spinning (HR-MAS) magnetic resonance spectroscopy
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Microalgae are a rich source of high value compounds such as carbohydrates, lipids, proteins and bioactive compounds. In particular, microalgae have been identified as a potentially important resource for carbon-capture and as a feedstock for green biofuels. Successful cultivation of microalgae can occur under a variety of nutrient and environmental conditions with each condition producing a unique distribution of compounds. In order to steer the cultivation towards a particular distribution of compounds, rapid and accurate methods for compound identification are required. Current methods for determining the absolute quantity of each component are time consuming and arduous making cultivation optimization impractical. High-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy offers a robust and rapid screening method capable of ascertaining the absolute quantity of each component with minimal sample manipulation. Sample preparation consists of harvested, centrifuged and freeze-dried whole-cell Nannochloropsis granulata from large-scale photobioreactors being accurately weighed and rehydrated with deuterium oxide and placed in an HR-MAS rotor. One-dimensional HR-MAS NMR spectra were recorded under quantitative conditions to determine the lipid and carbohydrate profile of the microalgae. The total time per sample for preparation, data acquisition and analysis was approximately 1 h. Changes in resonance profiles corresponding to varying proportions of saturated and polyunsaturated fatty acids were correlated to the time of harvest. In addition, standard two dimensional experiments were used to identify the major carbohydrate components. HR-MAS NMR spectroscopy has been used to profile the lipid and carbohydrate content of N. granulata and we have begun to establish methodologies for quality analysis/quality control for cultivation of various microalgal strains.
KeywordsHigh-resolution magic angle spinning Nannochloropsis granulata Nuclear magnetic resonance spectroscopy Whole-cell lipid profiling Quality assurance/quality control
Samples of N. granulata were obtained from Pat McGinn and Jenny MacPherson of the Institute for Marine Biosciences Marine Research Station. The authors thank Stephen O’Leary, Pat McGinn and Katie Dickinson for valuable discussions. Magnetic Resonance data was collected at the Biomolecular Magnetic Resonance Facility (BMRF) housed at the National Research Council of Canada's Institute for Marine Biosciences. The He-cooled probe for the 700 MHz NMR spectrometer at the NRC-IMB was provided by Dalhousie University through an Atlantic Canada Opportunities Agency Grant. This is NRC publication number 2011–54066.
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