High cellulase-free xylanases production by Moesziomyces aphidis using low-cost carbon and nitrogen sources

Background: Enzymes involved in xylan hydrolysis have several industrial applications. Selection of efficient microbial hosts and scalable bioreaction operations can lower enzyme production costs and contribute to their commercial deployment. This work aims at investigating the Moesziomyces aphidis yeast cultivation conditions that deliver maximal xylanase titres, yields and productivities using low-cost nitrogen (N) and carbon (C) sources. Results: NaNO₃ and KNO₃ supplementation improved xylanase production 2.9- and 2.7-fold (against 67.2 U mL⁻¹), respectively, using xylan as C source. Interestingly, the use of KNO₃, instead of NaNO₃, results in 2- to 3-fold higher specific activity, highlighting the potassium ion role. In addition, this study investigates synergetic effects on using ionic and organic N sources. A 4.9-fold increase in xylanase production, with high specific activity, is attained combining KNO₃ and corn steep liquor (CSL). Exploring the previous findings, this study reports one of the highest extracellular xylanase production titres (864.7 U mL⁻¹) by yeasts, using a media formulation containing dilute-acid pre-treated brewery spent grains (BSG), as C source and inducer, supplemented with KNO₃ and CSL. Replacement of dilute-acid pre-treatmed BSG by untreated BSG had low impact on xylanase production, of only 6%. Conclusion: Efficient production of M. aphidis xylanolytic enzymes, using low-cost N and C sources, is attractive for deployment of on-site enzyme production targeting different biotechnological applications under circular economy and biorefinery concepts. Potential xylanases end-users include industries such as brewing (using BSG as substrate for enzyme production), pulp and paper (benefiting from the cellulase-free xylanase activity) or lignocellulosic ethanol (for cellulase supplementation).