Enzymatic cell disruption of the microalgae Chlamydomonas reinhardtii for lipid and protein extraction

Microalgae has potential as a biofuel feedstock and as a source of valuable bioproducts for a variety of food, feed, nutraceutical, and pharmaceutical industries due to high yields of proteins, starch, and lipids. However, several challenges are associated with bioproduct extraction from microalgae. The complexity of microalgae cell walls necessitates use of energy intensive disruption methods, but current chemical or mechanical techniques can degrade economically valuable bioproducts. Therefore, disruption methods that target microalgae cell walls are essential, such as enzymatic biomass pretreatment for the release of specific biomolecules. Aqueous enzymatic pretreatment can preserve valuable bioproducts while permitting high levels of cell disruption. In this study, we optimized harvesting times that maximized protein yields in nitrogen depleted cultures and promoted lipid accumulation in the microalgae Chlamydomonas reinhardtii. Furthermore, an aqueous enzymatic assisted extraction (AEAE) treatment was developed. Four lytic enzymes were tested for their ability to permeate C. reinhardtii cell walls. Autolysin treatment was chosen as preferred cell disruption method. Treated cells were visualized by TEM imaging. TEM images and cell counts confirmed cell permeability (100%) and further cell lysis (50%) and product release when cells were treated with autolysin for 24 h. Biomass was also subjected to lipid and protein extraction after autolysin treatment and yields were compared to other mechanical and chemical extraction methods. Protein extractability was significantly enhanced by the autolysin pretreatment when compared to sonication pretreatment. Solvent extraction accompanied with autolysin biomass pretreatment significantly enhanced lipid extractable yields as compared to only solvent extraction and solvent plus sonication extraction.