Biological Signalling Supports Biotechnology: Cell Death Triggers Protein Release from Chlorella vulgaris

Multiple studies have demonstrated that following Pulsed Electric Fields (PEF) treatment, an incubation period exceeding 6 h in buffer is necessary to enhance the bio-accessibility of cell components such as proteins and lipids. This enhancement is primarily attributed to enzymatic processes activated during incubation, which facilitate the release of proteins and promote the solvent extraction of lipids from various microalgal species. The induction of this autolytic process can be triggered by various means, including dark anoxia, where microalgae are incubated in darkness for 24 to 48 h, or even by PEF treatment with very low specific energies (< 5 J/g). Notably, in Chlorella vulgaris, there's evidence suggesting the presence of a specific cell death inducing factor (CDIF) of protein origin, which triggers cell death in intact cells. The prevailing concept suggests that CDIF plays a pivotal role during the algae incubation period post-PEF treatment, prompting cell death and subsequent autolytic processes, thereby enhancing the extraction process. The search for the identity of the CDIF led to the assumption that radical oxygen species (ROS) may play a decisive role as signalling molecules, which are involved in many cell signalling pathways. ... mehrTo investigate this mechanism, we examined the intra- and intercellular ROS production during the incubation of fresh algal suspensions with algal extract containing CDIF, as well as with extract alone. While algal cell death induced by PEF treatment, even at low specific energies, resulted in a significant increase in intracellular ROS, no alterations in inter- and intracellular ROS were observed during cell incubation with CDIF-containing extract. This discrepancy may be attributed to the extract's antioxidant-rich composition, which not only contains CDIF but also suppresses ROS levels. This observation suggests that ROS depletion disrupts cell signalling pathways, ultimately leading to programmed cell death. To validate this hypothesis, we evaluated the cytotoxicity of antioxidants such as Trolox, glutathione, and ascorbic acid on algal cells at various concentrations. Surprisingly, ascorbic acid increased algal mortality over a 24 h incubation period and promoted the release of proteins, correlating with algal mortality. Based on these insights, we investigated the potential of enhancing the extraction process by combining PEF treatment with a subsequent incubation step in the presence of ascorbic acid. Our investigation unveiled a significant increase in protein yield compared to applying PEF treatment alone. This finding bears significance as the synergistic application of cell disruption and ascorbic acid not only enhances the yield of extracted cell components from algae but also shields them from oxidative degradation. This would allow for the development of new downstream processes that align with environmentally conscious practices, marking a significant step towards a more sustainable and efficient approach in biotechnological applications.