Harnessing brewing industry byproducts for sustainable β-glucosidase production by recombinant Saccharomyces cerevisiae

The sustainable recirculation of industrial microbial waste biomass into value-added products offers an eco-friendly and cost-efficient approach to biocommodity production. In this study, we evaluated four expression plasmids: yEN1-Pccbgl1, yEN1d-Pccbgl1, yIN2-Pccbgl1 and yEN2-Pccbgl1 for β-glucosidase activity in Saccharomyces cerevisiae. The recombinant S. cerevisiae Y294[EN1d-Pccbgl1] strain containing the small high copy number plasmid displayed the highest level of enzyme activity at 190 U/g DCW. In contrast, the strain harbouring the integrative plasmid, S. cerevisiae Y294[IN2-Pccbgl1], displayed the lowest enzyme activity at 9.5 U/g DCW. The best performing S. cerevisiae Y294[EN1d-Pccbgl1] strain was subsequently assessed for enzyme production using brewery waste streams as feedstock. Cultivating the recombinant strain in defined media resulted in a maximum β-glucosidase activity of ∼1.0 U/mL comparable to the activity obtained when using 10 g/L Komagataella pastoris or commercial S. cerevisiae biomass as nitrogen sources. Notably, activity increased to ∼2.0 U/mL when brewers' spent yeast was used as the nitrogen source. Furthermore, when brewers' spent grains and brewers' spent yeast were used as carbon and nitrogen sources respectively, 1.46 U/mL of β-glucosidase activity was obtained. This is comparable to levels obtained using brewers’ spent grains in combination with commercial cellulases. These findings highlight a promising biotechnological approach: repurposing low-cost, carbohydrate-rich industrial waste streams in conjunction with microbial biomass waste for the economical production of recombinant enzymes. This strategy not only reduces production costs but also contributes to waste valorisation and circular bioeconomy initiatives.