Autolytic enzymes for multiproduct microalgal biorefineries: tRIggERS DIGEST

Microalgae represent a more sustainable feedstock for producing functional food, feed, nutraceutical, and cosmetic ingredients. However, their commercial application is still confined to only a handful of niche markets due to the high costs associated with their cultivation and, more importantly, downstream processing (mainly product extraction and purification). Among these, the cell disruption stage contributes significantly to the overall downstream processing costs, requiring energy- and chemical-intensive unit operations. This is mostly due to the presence of a rigid cell wall characteristic of most of the microalgal species. Enzyme-assisted extractions have been proven to be a more sustainable way of performing these processes, by significantly reducing the amount of solvents and energy required to achieve high product extraction efficiency. However, the high costs of enzyme cocktails and lack of their reuse represent major bottlenecks limiting their application in commercial microalgal processes. To overcome this hurdle we propose to completely remove the need for a cell disruption processing step by including in the microalgal cells a self-destruct mechanism triggered by an external kill-switch signal such as exposure to a certain light spectrum. This will signal the microalgal cells to produce a specific enzymatic cocktail which will trigger their autolysis by attacking their membrane and cell wall. With the available microalgal genetic engineering toolbox, evaluation of the feasibility of inducible enzymatic microalgae cell wall disruption in microalgae biorefineries is critical. This system will provide the ultimate microalgal “cell factory” and offer a wider platform for producing a whole range of functional food and nutraceutical ingredients.