Book of Abstracts (PDF) - International Mycological Association

IMC7 Tuesday August 13th Lectures
199 - Biochemical and molecular aspects of lignin
degradation by Pleurotus species
A.T. Martínez 1* , F.J. Ruiz-Dueñas 1 , M. Perez-Boada 1 , P.
Ferreira 1 , S. Camarero 1 , F. Guillen 1 , M.J. Martínez 1 , T.
Choinowski 2 & K. Piontek 2
1 CIB, CSIC, Velazquez 144, E-28006 Madrid, Spain. -
2 ETHZ, Universitätstr. 16, Zurich, Switzerland. - E-mail:
ATMartinez@cib.csic.es
Pleurotus species are investigated due to their ability to
degrade lignin selectively. Their ligninolytic system is
different from that of the model white-rot basidiomycete
Phanerochaete chrysosporium. Extracellular
oxidoreductases have been characterized from Pleurotus
eryngii including versatile peroxidase (VP), aryl-alcohol
oxidase (AAO) and laccases. These enzymes are of
biotechnical interest for degradation of lignin, aromatic
compounds and dyes. P. eryngii laccases oxidize lignin via
natural redox mediators and contribute to oxygen activation
by redox cycling of lignin-derived quinones. AAO and VP,
which have been recently cloned, crystallized and
expressed in Escherichia coli and Emericella nidulans, are
characteristic of the ligninolytic system of Pleurotus (and
Bjerkandera) species. AAO provides hydrogen peroxide
for peroxidase activity and generation of active oxygen
species. VP represents a third type of ligninolytic
peroxidase combining the catalytic properties of lignin
peroxidase and manganese peroxidase (first described in P.
chrysosporium) due to an hybrid molecular architecture
including sites for oxidation of both Mn(II) and aromatic
substrates. AAO and VP molecular models were obtained
by homology modeling (using crystal structures as
templates), and the VP crystal structure has been recently
solved. Future studies include confirmation of active sites
by site-directed mutagenesis, and modulation of catalytic
properties by protein engineering techniques.
200 - Role of reactive oxygen species in wood decay by
fungi
K.E. Hammel
USDA Forest Products Lab, One Gifford Pinchot Drive,
Madison, WI 53705, U.S.A. - E-mail:
kehammel@facstaff.wisc.edu
Extracellular reactive oxygen species (ROS) have long
been thought to have a biodegradative function in wood
decay by fungi, but the nature of these species and the
mechanisms for their production have not been elucidated.
We monitored the hydroxylation of a synthetic aromatic
polymer, phenethyl polyacrylate, to estimate the magnitude
of extracellular ROS production by two brown rot
basidiomycetes, Gloeophyllum trabeum and Postia
placenta, on cellulose. The results showed that ROS
production was sufficient to account for much of the
cellulose depolymerization in the cultures. Both fungi
produced extracellular 2,5-dimethoxyhydroquinone, a
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Book of Abstracts
metabolite that rapidly reduces ferric iron and dioxygen,
thus yielding hydroxyl radicals via the Fenton reaction. We
purified and characterized a G. trabeum flavoprotein
NADH:quinone reductase that probably drives this
chemistry by regenerating the hydroquinone. The gene that
encodes the reductase shares substantial similarity with
quinone reductase genes of other fungi, including some
nonlignicolous species.
201 - Biotechnological applications of wood decay fungi
E. Srebotnik * , M. Weisgram & K. Messner
Institute of Chemical Engineering, Getreidemarkt 9, A-
1060 Vienna, Austria. - E-mail:
esrebot@mail.zserv.tuwien.ac.at
The ligninolytic systems of white-rot fungi have great
potential for applications in wood-processing such as
pulping, pulp bleaching and wood composite manufacture.
For example, the use of white-rot fungi to treat wood chips
prior to mechanical pulping (biopulping) is already
approaching industrial scale. Furthermore, the low
specificity of these systems allows for the conversion of
various aromatic pollutants and industrial wastes such as
contaminated soil (bioremediation). These processes
involve the use of white-rot fungi or their ligninolytic
enzymes to treat polycyclic aromatic hydrocarbons (PAH),
polychlorinated biphenyls and other hazardous xenobiotics.
Whether to apply living fungi or isolated enzymes will
depend on the specific properties of the material to be
treated. For example, biopulping takes advantage of the
fact that white-rot fungi not only produce a complete set of
enzymes but can also transport these enzymes into wood
chips and create the appropriate physiological conditions
for enzymatic reactions. However, processes involving
living organisms are relatively difficult to control. Thus,
the use of isolated enzyme systems would be preferable in
those cases, where the compounds to be treated are freely
accessible such as in soil extracts. This presentation will
give a brief overview of biotechnological applications of
white-rot fungi and their ligninolytic enzymes and discuss
in more detail the use of laccase for the bioremediation of
PAH.
202 - Some approaches to the evaluation of the white
rot basidiomycetes ligninolytic activity
V.I. Elisashvili * , E. Kachlishvili, N. Tsiklauri, T.
Khardziani & M. Bakradze
Institute of Biochemistry and Biotechnology, 10 km
Agmashenebeli kheivani,380059 Tbilisi, Georgia. - E-mail:
velisashvili@hotmail.com
Ligninolytic activity of basidiomycetes from different
taxonomic groups has been extensively. The production
patterns and levels of laccase and Mn-dependent
peroxidase (MnP) differed among species and strains of the