Microalgal swimming signatures as indicators of neutral lipids production across growth phases

Microalgae have been shown as a potential bioresource for food, biofuel, and pharmaceutical products. During the growth phases with corresponding environmental conditions, microalgae accumulate different amounts of various metabolites. We quantified the lipid accumulation and analyzed swimming signatures (speed and trajectories) of the motile green alga, Dunaliella primolecta, during the lag-exponential-stationary growth cycle at different nutrient concentrations. We discovered significant changes in neutral lipid content and swimming signatures of microalgae across growth phases. The timing of the maximum swimming speed coincided with the maximum lipid content and both maxima occurred under nutrient stress at the stationary growth phase. Furthermore, the swimming trajectories of microalgae signal the growth phase and corresponding intracellular lipid accumulation. Our results provide the potential exploitation of microalgal swimming signatures as indicators for the cultivation conditions and the timing of microalgal harvest to maximize the lipid yield for biofuel production. The findings can also be implemented to explore the production of food and antibiotics from other microalgal metabolites with low energy cost.