Microdevice for studying the in situ permeabilization and characterization of Chlamydomonas reinhardtii in lipid accumulation phase

International audience; Microalgae are considered as a renewable source of lipid-rich biomass feedstock for biofuels due to their high fatty acids content when cultivated in stress conditions (nitrogen starvation). Nevertheless the use of solvents in conventional extraction methods raises important environmental, health and safety issues. The application of Pulsed Electric Field (PEF) to electroporate microalgae is a promising alternative to traditional processes involved in lipid recovery, as it might permeabilize cell membrane, easing the access out of the cytoplasm, and reducing the use of solvents. In order to study the PEF effects on Chlamydomonas reinhardtii, we developed a microdevice that allows real time visualization during such electrical solicitation. A high number of electroporation chambers are designed on this biochip to characterize, in real-time, and in parallel, the permeabilization of cells subjected to PEF using the propidium iodide (PI). Several conditions were investigated (pulse energy, pulse duration and electrical field amplitude). Reduced energy consumption, heat effects and electrochemical reactions are obtained when applying short pulses (5 μs) of high electric field (4 to 6 kV·cm− 1). Moreover, an increase is observed in cell diameter and lipid content over time in nitrogen stress conditions. The cell sensitivity to the PEF seems to be affected by the cell diameter. Finally, for the first time, lipid droplet redistribution was observed within the cytoplasm during the treatment, showing that 5 μs pulses lead to additional intracellular electroporation effects.