Development of Novel Microfluidic Techniques for the Study of Microalgae at the Single-Cell Level

Abstract

Aquatic environments make up 70% of the total Planet Earth surface and marine phytoplankton is of crucial importance in the regulation of the climate as well as a key contributor to global geochemical cycles. Although marine microorganisms have been widely studied during decades, there exists a lack of quantification methods allowing for their in vivo and single-cell-level investigation. The complexity of the marine environment considering currents, pycnoclines and other different physicochemical phenomena, makes its recreation a difficult task. In order to overcome such complexities, we have studied three different microfluidic devices, here named: (i) Lagoon-like devices, (ii) Classical Mother Machine devices and (iii) Modified Mother Machine devices. Our main aim was to test the feasibility of each device in robustly growing Ostreococcus tauri (O. tauri), a model microalga for studies of alga-virus and alga-bacteria interactions and circadian rhythm. We successfully followed and observed O. tauri development within the Modified Mother Machine microfluidic device at the single-cell level. In addition, we also investigated the different life stages of the microalgal cells with a high image resolution. We were also able to observe the proliferation of bacteria within all three devices. This fact, however, the presence of bacteria, became a problem since they inhibited the normal growth of O. tauri cells. The main advantage of our system is that it allows for the long-term (up to 10 days) cultivation of single cells of the microalga under a well-controlled physical environment, as for instance: temperature, light irradiance, and medium supply. Our system has the potential to provide a single-cell resolution to different fields within aquatic microbiology, including, cell physiology, climate change effects on individual cells and the study of microbial interactions.