Valorization of fish waste and sugarcane bagasse for Alcalase production by Bacillus megaterium via a circular bioeconomy model

Background: The disposal of biomass waste from the agro-industry is a global challenge due to its negative environmental impacts. The global fishing industry and aquaculture in 2018 produced around 180 million tons of capture; however, ∼50% of fish tissues are disposed of. On the other hand, bagasse is a major by-product of the sugar industry. This study aims to valorize fish waste and bagasse. Methods: We managed to establish a Bacillus megaterium-based protein overexpression system using protease-hydrolyzed fish viscera as the growth medium for B. megaterium strain YYBM1 and using sugarcane bagasse-derived xylose to induce protein overexpression. Green fluorescent protein served as the model to optimize the system. Subsequently, we overexpressed a recombinant Alcalase, a thermostable alkaline protease, in strain YYBM1 following the optimized conditions. Significant findings: We achieved a maximum yield of 2.5 g Alcalase per kg fish viscera (dried weight), with a corresponding 20-fold reduction in production cost. The recombinant Alcalase efficiently hydrolyzed both strain YYBM1 cells and fish viscera at pH 9 and 60 °C, which allows a medium manufacturing process using autolyzed strain YYBM1 cells carrying Alcalase, bypassing the use of purified proteases. Our protein overexpression system represents an addition to the circular bioeconomy, buttressing the global call to develop innovative industries based on responsible consumption and production.