Book of Abstracts (PDF) - International Mycological Association

IMC7 Thursday August 15th Lectures
328 - Fungal influence on metal mobility: mechanisms
and relevance to environment and biotechnology
G.M. Gadd * , E.P. Burford, M. Fomina, F.A. Harper & H.
Jacobs
Division of Environmental and Applied Biology, Biological
Sciences Institute, School of Life Sciences, University of
Dundee, Dundee, DD4 1HN, Scotland, U.K. - E-mail:
g.m.gadd@dundee.ac.uk
In the terrestrial environment, fungi are of importance as
decomposer organisms and plant symbionts (mycorrhizas),
playing important roles in carbon and many other
biogeochemical cycles. For example, the ability of fungi to
solubilize insoluble metal phosphates is important for plant
and microbial nutrition. Metals and their derivatives can
interact with fungi in various ways depending on the metal
species, organism and environment, while fungal metabolic
activities can also influence speciation and mobility.
Certain mechanisms may mobilize metals into forms
available for cellular uptake and leaching from the system,
e.g. complexation with organic acids, other metabolites and
siderophores. Metals may also be immobilized by, e.g.
sorption onto cell components, exopolymers, transport and
intra- and extracellular sequestration or precipitation. The
relative importance of such apparently opposing
phenomena of solubilization and immobilization are key
components of biogeochemical cycles for toxic metals,
whether indigenous or introduced into a given location, and
fundamental determinants of fungal growth, physiology
and morphogenesis. Furthermore, several processes are of
relevance to environmental bioremediation. This
contribution seeks to highlight selected physico-chemical
and biochemical mechanisms by which fungi can interact
with and transform toxic metal species between soluble and
insoluble forms, and to draw attention to the environmental
significance of these processes.
329 - Molecular mechanisms induced upon cadmium
exposure in the ectomycorrhizal fungus Paxillus
involutus
M. Courbot 1* , C. Jacob 1 , P. Leroy 2 , A. Brun 1 & M. Chalot 3
1 Université Henri Poincaré Nancy I, Faculté des Sciences
et Techniques, UMR INRA-UHP 1136 'Interactions
Arbres/Micro-organismes', BP 239, 54506 Vandoeuvre-les-
Nancy Cedex, France. - 2 Laboratoire 'Thiols et fonctions
cellulaires' - Faculté de Pharmacie, BP 403, 54001 Nancy
Cedex, France. - 3 Centre INRA-Nancy, UMR INRA-UHP
1136 'Interactions Arbres/Micro-organismes', 54280
Champenoux, France. - E-mail: mikael.courbot@scbioluhp.nancy.fr
The response of mycorrhizal fungi to toxic metals is of
importance in view of their interest in the reclamation of
polluted sites and their importance in tree growth.
However, the molecular mechanisms underlying their
response towards metals remain poorly understood. We
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Book of Abstracts
have used the suppression substractive hybridization (SSH)
procedure combined to cDNA array hybridization, as well
as direct cloning to isolate genes which expression is
modulated by cadmium (Cd) in Paxillus involutus (Pi).
More particularly, we are investigating antioxidant and
detoxification enzymes such as those involved in free
oxygen radical scavenging, in glutathione and chelating
agents biosynthesis. The increasing activity of the Pi
superoxide dismutase as well as the fact that it can
functionally substitute for the E. coli SODs under Cd stress
suggests that this enzyme is involved in the cellular
response of Pi to Cd. The transcript levels of gglutamylcysteine
synthetase, GSH synthetase,
metallothioneins, thioredoxins and tyrosinase were
measured. Of these, metallothioneins and tyrosinase were
shown to be highly regulated by Cd. The intracellular pools
of amino acids, glutathione, gamma-glutamate-cysteine and
different phytochelatins in Pi were also subjected to
changes under Cd exposure. The isolation of genes and
proteins involved in the response to cadmium-induced
stress open new perspectives in the understanding of
molecular mechanisms that promote tolerance in
mycorrhizal fungi.
330 - Interactions of ericoid mycorrhizal and soil fungi
with heavy metals: implications for tolerance and
bioremediation
E. Martino 1* , S. Cerminara 1 , P. Bonfante 2 & S. Perotto 1
1 Dipartimento di Biologia Vegetale, Università di Torino,
Viale Mattioli 25, 10125, Torino, Italy. - 2 Istituto per la
Protezione delle Piante del CNR, Sezione di Torino, Viale
Mattioli 25, 10125, Torino, Italy. - E-mail:
elena.martino@unito.it
Ericoid mycorrhizal fungi increase the ability of their host
plants to colonize soils polluted with toxic metals, although
the underlying mechanisms are unclear. We investigated
the molecular and cellular responses of ericoid mycorrhizal
fungi to heavy metals, and found a novel range of
extracellular proteins being produced in the presence of
different soluble metal compounds. Some of these proteins
were identified by N-terminus sequencing as antioxidant
enzymes (e.g. superoxide dismutase, SOD). SOD enzymes
play a pivotal role in stress responses and are involved in
metal tolerance. We also found that ericoid mycorrhizal
fungi can solubilize insoluble metal compounds thanks to
the release of organic acids. Solubilization activity was not
the same for all the strains tested, with isolates from
unpolluted soils being more efficient in the solubilization
process than those from metal polluted soils. We are also
exploring the potential of ericoid mycorrhizal and other
soil fungi to mobilize iron from a very specific insoluble
substrate: asbestos fibers. These fibers contain variable
amounts of iron, one of the most relevant chemical features
in the mechanism of asbestos carcinogenicity. Iron
extraction from asbestos may thus decrease their cytotoxic
potential. Our results suggest that some fungal species can
remove significant amounts of iron from the fibers, thus
opening new perspectives for the decontamination of
asbestos-contaminated sites.