ASPERGILLI AND LIGNOCELLULOSICS - ENZYMOLOGY AND BIOTECHNOLOGICAL APPLICATIONS

Aspergilli are versatile ascomycetes that are able to transform at a r apid rate a wide spectrum of lignin-related aromatic compounds. While it is clear that these fungi can degrade phenolic and polysaccharide c omponents from lignocellulosic material, the status regarding degradat ion of high-molecular mass lignins is controversial. This review compi les data from the literature as well as that from the authors' laborat ory with the aim of clarifying this point. The main body of evidence p oints towards the inability of aspergilli alone to degrade lignin free of low-molecular mass contaminants. Nevertheless, the ability of this genus to efficiently degrade hemicelluloses makes it an essential par ticipant in the complex microbial system necessary for wood decay unde r natural conditions. Aspergilli are known to overproduce high levels of hemicellulolytic enzymes. Out of the large array of these enzymes t hat act in concert to degrade lignocellulosic material, only endoxylan ases of aspergilli are described in so far as these are the main activ ities required for enzyme-aided bleaching. The biochemical features of the endoxylanases from Aspergillus niger are briefly described as the se serve to illustrate how a complex family of isozymes is necessary t o deal with the structural and chemical heterogeneity of xylans. Empha sis is placed on the biotechnological applications of lignocellulosic materials transformed by aspergilli. The key application areas are bio pulping and biobleaching where a reduction in the use of environmental ly harmful chemicals traditionally used in the pulp and paper industry is envisaged. Waste water treatment represents another vast applicati on area where aspergilli have been shown to be effective not only in c olour removal but also in the bioconversion of potentially noxious sub stances into useful bioproducts.