Quantitative tracking of the growth of individual algal cells in microdroplet compartments

In this paper we introduce a simple droplet-based microfluidic system consisting of two separate devices to encapsulate and culture microalgae, in contrast to cultivation in bulk liquid medium. This microdroplet technology has been used to monitor the growth of individual microalgal cells in a constant environment for extended periods of time. Single cells from three species of green microalgae, (two freshwater species Chlamydomonas reinhardtii and Chlorella vulgaris, and one saline species Dunaliella tertiolecta), were encapsulated and incubated in microdroplet compartments of diameter of ∼80 μm, and their growth analysed over 10 days. In all cases, the doubling time of microalgae grown in microdroplets was similar to growth in bulk. The growth of C. reinhardtii in microdroplets of varying diameters and with different initial cell numbers per droplet was investigated, as well as the effect of varying medium conditions such as pH and nitrogen concentration. This methodology offers the opportunity to study characteristics over time of individual cells and colonies, as well as to screen large numbers of them.