Single cell lipid profiling of Scenedesmus quadricauda CASA-CC202 under nitrogen starved condition by surface enhanced Raman scattering (SERS) fingerprinting

Oleaginous microalgae tend to accumulate neutral lipids as their energy reserve mainly in the form of triacylglycerol (TAG) which can be utilized as the precursor molecule for biodiesel and other nutraceutical application. The TAG level and the fatty acid composition of microalgae modulated by exposing the algal strains to different physicochemical, nutritional and environmental factors. Nitrogen starvation is considered as an important and practically feasible way by which the lipid content can be enriched in large scale production. In the present investigation, Scenedesmus quadricauda CASA-CC202, oleaginous microalgae with high biomass productivity has been subjected to nitrogen starvation and the stress mediated lipids were analyzed on a single cell basis. As a new insight, we have successfully identified the unsaturated and saturated functionalities of fatty acids by surface enhanced Raman scattering (SERS) spectral footprint under nitrogen starved condition in acidic and, neutral pH. In addition, other macromolecules like chlorophyll, carotenoids, proteins and carbohydrates were also selectively mapped. Most promising SERS mapping pattern of single algal cells depicts high lipid rich component under nitrogen starved condition and degree of unsaturation vs. saturation has been validated through SERS spectral analysis by comparing with the Raman spectra of standard fatty acids. Moreover, the present investigation, clearly distinguish the lipids from other macromolecules like protein, carbohydrate and photosynthetic pigments in whole cell. Finally, SERS based analysis dually by spectral and mapping techniques of lipid enriched S. quadricauda CASA-CC202 has been superimposed with Nile red staining of the same algal cells which unambiguously identify the neutral lipid components under the starved condition.