Abstract
BackgroundLipid/carbohydrate content and ratio are extremely important when engineering algal cells for liquid biofuel production. However, conventional methods for such determination and quantification are not only destructive and tedious, but also energy consuming and environment unfriendly. In this study, we first demonstrate that Raman spectroscopy is a clean, fast, and accurate method to simultaneously quantify the lipid/carbohydrate content and ratio in living microalgal cells.ResultsThe quantification results of both lipids and carbohydrates obtained by Raman spectroscopy showed a linear correspondence with that obtained by conventional methods, indicating Raman can provide a similar accuracy to conventional methods, with a significantly shorter detection time. Furthermore, the subcellular resolution of Raman spectroscopy enabled not only the concentration mapping of lipid/carbohydrate content in single living cells, but also the evaluation of standard deviation between the biomass accumulation levels of individual algal cells.ConclusionsIn this study, we first demonstrate that Raman spectroscopy can be used for starch quantification in addition to lipid quantification in algal cells. Due to the easiness and non-destructive nature of Raman spectroscopy, it makes a perfect tool for the further study of starch–lipid shift mechanism.
Highlights
Lipid/carbohydrate content and ratio are extremely important when engineering algal cells for liquid biofuel production
Conventional lipid/carbohydrate quantification methods For the quantification of lipid/carbohydrate content, every culture batches that underwent the same treatment were dispensed into two parts, one part for Raman microscopy imaging and the other part for total carbohydrate quantification [16] and fatty-acid transesterification coupled with gas chromatography (GC)/mass spectrometry (MS) quantification [17]
Due to the nature of such baseline assumption, negative peak intensity values could appear in the Raman images, but we present and calculate only the positive values
Summary
Lipid/carbohydrate content and ratio are extremely important when engineering algal cells for liquid biofuel production. They are ideal sources for biofuel production that does not compete for arable land with edible crops, and can grow well under various wastewaters with high uptake rates of enormous pollutants [1, 2] To enhance their economic feasibility, much effort has been made to optimize the cultivation strategies [3] or to engineer the synthesis pathways of energy-rich metabolites, i.e., lipids and Currently, the most widely used technique to quantify the lipid and carbohydrate content in microalgae is gas chromatography (GC) or liquid chromatography (LC) coupled with mass spectrometry (MS). Since the GC/MS or LC/MS methods inevitably involves the chemical extraction of specific compounds (e.g., fatty acid and simple sugars) in the first step, it takes hours of labor work to quantify the lipid/carbohydrate content of a batch of microalgae They are considered as destructive, time- and labor-consuming, and environment-unfriendly methods [9]. Its real impact lies in the simultaneous quantification of multiple components in an easy, fast, and accurate manner
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