Profiling lipid and protein co-production in the microalgaeChlamydomonas reinhardtiiand the novel application of autolytic enzymes as an extraction pretreatment

Abstract

Abstract. Economic and life cycle assessment studies of microalgae as a biofuel feedstock have shown that oil extraction and recovery limit the commercialization of microalgal derived biofuels. Current methods include the use of solvents and energy-intensive mechanical processing which, among other disadvantages, leads to degradation of secondary bioproducts during extraction. The use of aqueous enzymatic extraction (AEE), a non-solvent and environmentally friendly recovery method, provides an opportunity to design an integrated process for oil and protein extraction. Due to current approaches that focus only on a single bioproduct, combined lipid and protein profiling over time is needed in order to optimize both yields. Secondly, regarding AEE, it is necessary to consider enzyme costs and extraction efficiency to make it viable when compared to mechanical and chemical methods. This leads to another challenge in the AEE process, which is the need to adjust variables such as pH and temperature in the culture media in order to maximize enzyme activity. A potential alternative to address this issue is the use of autolytic enzymes. These enzymes are produced and secreted into the culture media by particular algae species under stress conditions. In this study, we evaluated the potential use of the microalgae C. reinhardtii as a feedstock for aqueous enzymatic oil and protein extraction, using an autolytic enzyme produced by the same algae specie, as part of the extraction process. First, we analyze lipid and protein accumulation kinetics in nitrogen-depleted cultures. Second, we evaluate the lytic activity of different enzyme treatments. Finally, we compare lytic activity of the treatments above with the autolytic enzyme produced by C. reinhardtii. Results indicated maximum oil and protein yields were achieved after 48 hours under nitrogen depleted conditions. Moreover, cell wall lysis was achieved after 2 hours of autolysin treatment at room temperature (25°C ± 5) and an optimal pH between 7.5 and 8.2.