Jc. Duarte et M. Costaferreira, ASPERGILLI AND LIGNOCELLULOSICS - ENZYMOLOGY AND BIOTECHNOLOGICAL APPLICATIONS, FEMS microbiology reviews, 13(2-3), 1994, pp. 377-386
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.