Impact of pulsed electric fields and mechanical compressions on the permeability and structure of Chlamydomonas reinhardtii cells

Sakina Bensalem,Filipa Lopes,Bruno Le Pioufle,Bertrand Cinquin,Dominique Pareau,Olivier Français

doi:10.1038/s41598-020-59404-6

Abstract

Current research findings clearly reveal the role of the microalga’s cell wall as a key obstacle to an efficient and optimal compound extraction. Such extraction process is therefore closely related to the microalga species used. Effects of electrical or mechanical constraints on C. reinhardtii’s structure and particularly its cell wall and membrane, is therefore investigated in this paper using a combination of microscopic tools. Membrane pores with a radius between 0.77 and 1.59 nm were determined for both reversible (5 kV∙cm−1) and irreversible (7 kV∙cm−1) electroporation with a 5 µs pulse duration. Irreversible electroporation with longer pulses (10 µs) lead to the entry of large molecules (at least 5.11 nm). Additionally, for the first time, the effect of pulsed electric fields on the cell wall was observed. The combined electrical and mechanical treatment showed a significant impact on the cell wall structure as observed under Transmission Electron Microscopy. This treatment permits the penetration of larger molecules (at least 5.11 nm) within the cell, shown by tracking the penetration of dextran molecules. For the first time, the size of pores on the cell membrane and the structural changes on the microalgae cell wall induced by electrical and mechanical treatments is reported.

Highlights

Microalgae are currently recognized as a potential renewable source of proteins, pigments and lipids with a broad range of industrial applications[1]
C. reinhardtii cells were submitted to three different pretreatments: Pulsed electric field (PEF), a combination of PEFs with cyclic mechanical compressions and a combination of PEFs with an increased mechanical compression
The combined pretreatments included this first step of PEF, followed by mechanical compressions where the cells are flowed within successive microfluidic constrictions of 5 μm

Summary

Introduction

Microalgae are currently recognized as a potential renewable source of proteins, pigments and lipids with a broad range of industrial applications (cosmetics, food and feed, chemical, ...)[1]. When cultured under nitrogen starvation, some microalgae accumulate large amounts of neutral lipids in the form of droplets in the cytoplasm They are considered as a promising renewable source of energy and a potential alternative to traditional fossil fuels[2,3]. A pretreatment consisting of cell disruption before placing microalgae in contact with a solvent is commonly used in order to improve extraction[9,10]. This pretreatment is of utmost importance as the quantity and quality of the compounds obtained from the microalgae are very dependent on the treatments used. The chosen treatment must take into account the microalgal strain used Both steps of cell disruption and lipid extraction remain highly expensive[11]. Comprehensive studies of the microalgae’s cell wall structure in the context of an extraction process using pretreatments are currently poorly investigated

Methods

Results

Conclusion