Measurement of Lipid Droplet Accumulation Kinetics in <i>Chlamydomonas reinhardtii</i> Using Seoul-Fluor

Alternative energy resources have become an important issue due to the limited stocks of petroleum-based fuel. Microalgae, a source of renewable biodiesel, use solar light to convert CO₂ into lipid droplets (LDs). Quantification of LDs in microalgae is required for developing and optimizing algal bioprocess engineering. However, conventional quantification methods are both time and labor-intensive and difficult to apply in high-throughput screening systems. LDs in plant and mammalian cells can be visualized by staining with various fluorescence probes such as the Nile Red, BODIPY, and Seoul-Fluor (SF) series. This report describes the optimization of LD staining in <i>Chlamydomonas reinhardtii</i> with SF probes via systematic variations of dye concentration, staining time, temperature, and pH. A protocol for quantitative measurement of accumulation kinetics of LDs in <i>C. reinhardtii</i> was developed using a spectrofluorimeter and the accuracy of LD size measurement was confirmed by transmission electron microscopy (TEM). Our results indicate that our spectrofluorimeter-based measurement approach can monitor kinetics of intracellular LDs (in control and nitrogen-source-starved <i>Chlamydomonas reinhardtii</i>) accumulation that has not been possible in the case of conventional imaging-based methods. Our results presented here confirmed that an SF44 can be a powerful tool for <i>in situ</i> monitoring and tracking of intracellular LDs formation.