Biooxidación avanzada de compuestos modelo de lignina y contaminantes por el hongo ligninolítico Pleurotus eryngii

Resum

ABSTRACT Lignin, along with cellulose and hemicellulose, constitute the major components of plant cell walls. The degradation of the lignocellulose is a natural process of recycling of organic matter in which different types of organisms take part, but its colonization in Nature is mainly produced by basidiomycete fungi, group including the white rot fungi. This kind of fungi is characterized by their ability to effectively degrade all components of wood, including lignin. Its ligninolytic system is constituted by several types of enzymes (laccases, peroxidases, oxidases and reductases), whose ability to oxidize lignin includes a direct and indirect mode of action. The latter involves the production of ligninolytic agents of low molecular weight and high redox potential that play a fundamental role in the initial alteration of the structure of lignocellulose, required for the penetration of degradative enzymes. These agents include hydroxyl (·OH) radicals. Among the various mechanisms of ·OH production that ligninolytic fungi possess is the one generated through the establishment of redox cycles of quinones produced during the degradation of lignin. For the establishment of the redox cycle and the production of ·OH, it is sufficient to incubate the fungus in the presence of a quinone and suitably chelated Fe3+. In this work, the optimization of the production of ·OH, through the aforementioned mechanism, by the ligninolytic fungus Pleurotus eryngii has been approached, and the effect of the age of culture, the chelating agent of Fe3+ and the type of quinone were the criteria taking into account for the evaluation. After the optimization of ·OH production through redox cycle of quinones, the effect of these radicals on the ligninolytic activity of the fungus was evaluated. The work carried out was addressed to the study of the degradation of non-phenolic lignin model compounds as well as to the implication of ·OH on its Cα-Cβ bond cleavage. It was shown that P. eryngii is only able to degrade the compounds when ·OH production is induced. Among others, the degradation of the compounds by ·OH yielded veratraldehyde, characteristic intermediate product of the Cα-Cβ cleavage, revealing the implication of ·OH in the reaction. The effect of inducing ·OH production in P. eryngii on its ability to degrade a large number of organic pollutant compounds (dyes and BTEX) was subsequently evaluated. This induction was shown to enable the fungus to degrade compounds which cannot be oxidized by their enzymes and greatly accelerates the degradation of all others. These results allow us to consider the induction in P. eryngii of extracellular production of ·OH as a good strategy for the removal of contaminants and could be exemplified as an advanced bio-oxidation process.