Biological signals support biotechnology -increasing protein yield by triggering cell death in Chlorella vulgaris through algae extract

In our previous work, we found that Chlorella vu/garis extract obtained by physical cell disruption contains a factor that causes viable cultures to die within 24 h. This so-called death factor is synthesised by C. vulgaris mainly during the stationary growth phase and is more likely to be a protein or a set of proteins. Since the sensitivity of the recipient cells and the synthesis of this factor by the donor cells depend on the stage of the cell cycle, it was concluded that the cell death is triggered by a biological signalling process. So far, it is not known exactly which molecules are involved in the signalling process that triggers cell death. However, this effect can be used to reduce the specific treatment energy during pulsed electric field (PEF) treatment. This is because, as soon as some algal cells are inactivated by the PEF treatment and the death factor is released, intact cells are also dying, leading to an increased release of intracellular components. As a result, this low-energy PEF treatment with subsequent incubation time can be used as an energy-efficient method for extracting soluble proteins and lipids in a cascade process. ... mehrHowever, it is necessary to understand the mechanisms involved in this process to apply the method to other algal strains and to improve downstream processing of algal biomass. Based on our experimental data we identify two possible mechanisms that could explain how cell death in C. vulgaris is triggered by protein extracts. The first mechanism is based on a ligand-receptor interaction that led to programmed cell death (PCD) in C. . vulgaris. To verify this pathway protein purification and subsequent activity-guided protein fractionation was performed to identify the death factor. From a set of 29 proteins, two candidates were considered as they are involved in protein degradation and potential release of signalling molecules related to plant damage-associated molecular patterns. A second mechanism involves proteases and catabolic amino acid metabolism, accompanied by the release of reactive oxygen species (ROS). In this case, the oxidation of amino acids by LAAOs triggers a lethal ROS burst. However, measurements of inter-and intracellular ROS levels showed that this mechanism is unlikely, suggesting that there is an alternative model of induced cell death without the involvement of a ROS burst. lt appears that cell death induced by a protein extract is not related to a regular PCD pathway and signaling molecules, so further studies are needed to clarify this important question.