Desenvolvimento de estratégia biológica para a degradação de microcistina-LR e inibição celular de Microcystis aeruginosa

Abstract

Laccases are multicopper oxide reductase enzymes studied for their potential in degrading environmental contaminants such as dyes, drugs, and aromatic compounds. The reason lies in their mechanism of action, which involves the abstraction and transfer of electrons from the substrate, using oxygen as the final acceptor and generating water as the final product. Laccases can be produced by various organisms such as plants, bacteria, and especially fungi. White rot fungi are studied in enzyme production such as lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase (Lac), extracellular enzymes capable of mineralizing wood compounds such as lignin. Cyanobacteria, despite their ecological importance, certain species, such as Microcystis aeruginosa, produce toxins such as microcystin-LR (MC-LR), a contaminant that is difficult to remove by conventional treatment methods. The occurrence of cyanobacteria in water sources and reservoirs, together with the presence of cyanotoxins in drinking water, has become an increasingly frequent environmental and public health concern. This study evaluated the effectiveness of the crude enzyme extract produced by the fungus Trametes villosa in the biodegradation of MC-LR and analyzed its impacts on cyanobacterial growth. The lacase activity obtained (4,736 ± 306.5 U/L) was consistent with the values reported in the scientific literature, indicating that the semisolid medium using agro-industrial waste was capable of producing laccase. The concentration of microcystin-LR reported after solid-phase extraction averaged 0.197 mg/L, which is in accordance with references. The crude enzyme extracts were able to reduce the initial concentration of MC-LR in the samples by 25%, proving to be more effective than commercial lacase from Aspergillus sp. The cell inhibition experiment with the enzyme extract reduced the cell concentration of M. aeruginosa by 99% from the 11th day onwards, while commercial lacase decreased it by 76% in the same period, as did the inoculum of T. villosa fungal cells, which inhibited cyanobacterial growth by 79% in 11 days. Concluding that white rot fungi and their extracellular enzymes can contribute to the removal of microcystin-LR and Microcystis aeruginosa cells in aquatic environments. They indicate the possibility of using fungal laccases in the degradation of aquatic toxins and in the control of cyanobacterial blooms, contributing to the development of effective clean biotechnological solutions, contributing to the treatment of effluents and environmental remediation.