Avaliação das enzimas lacase e protease na biodegradação de microcistina

Abstract

Cyanobacteria are microorganisms capable of releasing toxins with different degrees of toxicity (cyanotoxins) when facing situations of abiotic stress. Microcystins are cyanotoxins known to be produced by cyanobacteria and can be found in different aquatic environments, including public supply reservoirs. The presence of microcystins in reservoirs causes great concern since microcystins are harmful to human health, both by ingestion and by direct contact. In the water treatment process, microcystins can be removed either by the use of activated carbon or by other methods such as AOP (Advanced Oxidative Process). However, both methods can generate additional residues, such as carbon adsorbed from toxins or by-products of the AOP degradation process. In this context, the objective of the present work was to evaluate the application of laccase and protease as enzymatic methods for microcystin biodegradation. The enzymes used were obtained from the cultivation of three fungal species: Trametes villosa for the laccase enzyme and Aspergillus brasiliensis and Trichoderma sp. For the protease enzyme. As a positive control, commercial Aspergillus sp laccase enzyme and commercial Trypsin protease were used. The microcystin samples were obtained by laboratory cultivation of Microcystis aeruginosa, which were submitted to the enzymatic biodegradation assay and subsequent quantification by high performance liquid chromatography (HPLC). The effect of enzymes on the growth of Microcystis aeruginosa was also evaluated. The maximum production of crude laccase in semi-solid culture with T. villosa was 3,929 U/L. Regarding the production of proteases, a maximum activity of 53 U/mL was observed in culture with Aspergillus brasiliensis and of 214 U/mL with Trichoderma sp. The biodegradation results showed maximum removal of 98.61% of the initial concentration of microcystin with the application of T. villosa laccase and 99.63% with commercial protease, under agitation conditions at 120 rpm and 37°C for 2 h 30 min. There was inhibition of the growth of M. aeruginosa with the use of the crude extract containing the enzyme T. villosa laccase at the end of 15 days of incubation on a bench at 21 °C and 25 °C. The results are promising regarding the use of fungal enzymes in the biodegradation of microcystin and inhibition of cyanobacterial growth, which provides a basis for studies and future applications.