Bundling the removal of emerging contaminants with the production of ligninolytic enzymes from residual streams

Enzymes offer interesting features as biological catalysts for industry: high specificity, activity under mild conditions, accessibility, and environmental friendliness. Being able to produce enzymes in large quantities and having them available in a stable and reusable form reduces the production costs of any enzyme-based process. Agricultural residues have recently demonstrated their potential as substrates to produce ligninolytic enzymes by different white rot fungi. In this study, the biotechnological production of a manganese peroxidase (MnP) by Irpex lacteus was conducted through solid-state fermentation (SSF) with wheat straw as substrate and submerged fermentation (SmF) employing wheat straw extract (WSE). The obtained enzyme cocktail also showed manganese-independent activity (MiP), related to the presence of a short MnP and a dye-decolorizing peroxidase (DyP) which was confirmed by shotgun proteomic analyses. In view of the enhanced production of ligninolytic enzymes in SmF, different parameters such as WSE concentration and nitrogen source were evaluated. The highest enzyme titers were obtained with a medium formulated with glucose and peptone (339 U/L MnP and 15 U/L MiP). The scale-up to a 30 L reactor achieved similar activities, demonstrating the feasibility of enzyme production from the residual substrate at different production scales. Degradation of five emerging pollutants was performed to demonstrate the high oxidative capacity of the enzyme. Complete removal of hormones and bisphenol A was achieved in less than 1 h, whereas almost 30% degradation of carbamazepine was achieved in 24 h, which is a significant improvement compared to previous enzymatic treatments of this compound.

Automated summary

Enzymes have been proven to be effective biological catalysts in various industries. By utilizing agricultural residues as substrates, high amounts of enzymes can be produced, providing a cost-effective and sustainable solution for enzyme-based processes. In this study, a specific enzyme, manganese peroxidase (MnP), was successfully produced using wheat straw as a substrate in both solid-state and submerged fermentation. The enzyme cocktail also exhibited manganese-independent activity (MiP), indicating the presence of other enzymes such as short MnP and dye-decolorizing peroxidase (DyP). The production of ligninolytic enzymes was further enhanced in submerged fermentation, and the optimal conditions for enzyme production were determined. Additionally, the enzymes showed a high oxidative capacity, as demonstrated by the degradation of five emerging pollutants. The complete removal of certain pollutants, such as hormones and bisphenol A, was achieved in a short period of time, highlighting the potential of these enzymes for environmental applications.