Papain production: Lactic acid bacteria as microbial cell factories for food-grade enzyme production

Abstract

Papain is an enzyme of wide industrial and pharmaceutical use that, even after 40 years of production, is still extracted from papaya crops. In this research project, we intend to use modern molecular biology tools in the construction of an efficient biotechnological production route of papain in a non-model microorganism. This approach represents a science frontier in terms of using different areas that are not normally related. A lactic acid bacterium will be selected to be genetically modified to become a host for the production of papain from brewer's spent grains using solid-state fermentation. Lactic acid bacteria (LAB) have several advantages for the production of enzymes over the use of typical cell factories, such as E. coli or S. cerevisiae, including simple metabolism, small genomes with reduced redundancy, fast growth, high sugar uptake rates, the potential for uncoupling of growth and energy metabolism, scarcer high-level control systems and generally recognized as safe microorganisms. The proposal has an economic, sustainable, societal and scientific impact since it creates new possibilities for the use of LAB as food-grade production and wastes valorisation through the use of brewer's spent grains. This serves as a suitable and low-cost substrate for the microorganism and contributes to the green economy by valorising waste streams and reducing carbon emissions, as related to the discharge of the residue. As an outcome, it is expected to develop useful tools in the efficient modification of LAB to be used as microbial cell factories for the production of enzymes, specially papain, while using agroindustrial residues as a substrate in the fermentation process.