Laccases from New Fungal Sources and Some Promising Applications

Abstract: Fungi are a group of organisms with the ability to produce different types of enzymes in order to get access to nutrients. Among the enzymes, oxidoreductases have the ability to degrade lignocellulosic material via an oxidative mechanism, facilitating the uptake of cellulosic material, which will be metabolized using other enzymes to provide the required nutrients to the fungi. Ecologically, oxidoreductases play an essential role in the mobilization of carbon into the ecosystem. Laccase is an oxidative enzyme that has the ability to oxidize lignin using molecular oxygen, which is reduced to water. The oxidative ability of laccases is employed in a number of industrial and environmental applications including bioremediation, food technology, nanotechnology, medicine, pulp and paper industry, and cosmetology. Owing to its versatility, laccase is continuously under investigation for new applications.
The present thesis reports on new sources of fungal laccase as well as novel laccase applications.
Fusarium sp. BOL35 is an ascomycete fungus, isolated from the Bolivian Amazonas. It was found to produce laccase when it was cultivated to degrade benzo[a]pyrene (a polycyclic aromatic hydrocarbon) indicating a possible potential of laccase in the degradation of xenobiotic compounds.
Galerina sp. HC1 was also isolated from the Bolivian Amazonas and was selected as a laccase producer. This fungus is easy to grow in submerged cultivation as well as in solid state fermentation for laccase production. Galerina sp. HC1 laccase has been shown to have a potential application in dye decolorization as well as in demethylation of lignin, which opens up the possibility to use this fungal laccase in various biotechnological applications.
Trametes versicolor laccase has been used to decolorize textile dyes in a membrane reactor system. The enzyme is capable of catalyzing fast decolorization reactions in the presence of natural mediators. Moreover, it is able to catalyze decolorization in the presence of an immobilized mediator, opening up the possibility of recycling both the enzyme and the mediator.
Trametes versicolor laccase has in the presence of a mediator (TEMPO) been shown to catalyze oxidation of primary alcohols on polysaccharide gel to produce the corresponding aldehydes. The oxidized Sepharose was applied for protein immobilization and was found to be as effective as the gel oxidized with periodate.