Book of Abstracts (PDF) - International Mycological Association

IMC7 Thursday August 15th Lectures
308, 1098 SM Amsterdam, The Netherlands. - E-mail:
teixeira@science.uva.nl
The metabolic network of the living cell is endowed with
an amazing capacity to cope with different environmental
conditions. This capacity is due to a variety of signal
transducing and regulatory systems designed to tune the
cell's metabolic machinery to prevailing physico-chemical
conditions e.g. nutrient availability, temperature,
osmolarity and the nature of the energy source. Although
the mechanisms that underly various adaptive responses
may differ in many respects, they seem to have in common
that the energetic and redox state of the cell is crucial to
their functioning on the one hand and that they affect
energy and redox catabolism on the other. In this context, it
will be shown that the extent to which exponentially
growing cells can withstand a heat shock is related to the
ATP pools and to their potential to adapt the internal
trehalose and glycogen metabolism. Further, a quantitative
flux analysis of strains modified in the levels of proteins
(hap4p and hexokinase 2) that take part in general glucose
repression regulatory pathways, will illustrate the role of
these pathways in the bioenergetics of yeast growth and
maintenance. Finally, we will present an example of the
transient transcriptional and physiological events which are
invoked when steady state glucose-limited chemostat
cultures are challenged with oleate as energy source. Here
again, the initial adaptive response (prior to peroxisome
biosynthesis) is gouverned by redox and energetic
imbalance.
342 - Uptake and catabolism of glucose
M. Mattey
University of Strathclyde, 204, George Street, Glasgow G1
1XW, Scotland, U.K. - E-mail: m.mattey@strath.ac.uk
Fungi are chemoheterotrophs found in a variety of habitats
and their life cycles are similarly varied. Strategies adopted
by fungi vary from typical 'r' strategists, with a high
reproductive rate and a short life cycle, to 'K-'strategists
which use resources efficiently and reproduce more slowly.
Whatever their environmental niche most fungi can use
glucose and do so with the same basic biochemistry. The
uptake of glucose uses members of the major facilitator
superfamily which mediate the thermodynamically
downhill movement of glucose across the cell membrane.
Free glucose within the cell is maintained at a low level by
hexokinase, which also confines the subsequent
metabolism to the cell by phosphorylation. Glycolysis is
the most common pathway for the degradation of glucose.
Although the basic biochemistry is the same in most cases,
the regulation of the enzymes differs for different
strategies. Faced with a surfeit of glucose, a situation that
may occur naturally or in industrial processes, fungi grow
rapidly, but this may not be enough to use all the glucose
that enters the cell by simple diffusion. The rate of
diffusion can exceed the maximum uptake rate of
facilitated transport. When this happens facilitated
transport appears to shut down by an unknown mechanism,
and free internal glucose levels rise. In the opposite
situation, with oligotrophic media, the problem becomes
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Book of Abstracts
one of how to maintain internal metabolite levels when the
entry rate is less than the flux.
343 - Galactose metabolism in Trichoderma and
Aspergillus: properties, regulation and identification of
a second, reductive pathway
B. Seiboth 1 , L. Karaffa 2 & C.P. Kubicek 1*
1 Section Microbial Biochemistry and Gene Technology,
Institute of Chemical Engineering, TU Wien,
Getreidemarkt 9/166, A-1060 Wien, Austria. - 2 Department
of Microbiology and Biotechnology, Faculty of Sciences,
University of Debrecen, H-4010, P.O.Box 63, Debrecen,
Hungary. - E-mail: ckubicek@mail.zserv.tuwien.ac.at
D-Galactose metabolism via the Leloir pathway is a
ubiquitous trait in pro- and eukaryotic cells. Its metabolic
regulation has been extensively studied in yeast
(Saccharomyces, Kluyveromyces) but not in filamentous
fungi. A more detailed knowledge on the latter would be
worthwhile, as lactose (1,4-0-β-D-galactopyranosyl-Dglucose)
arising from whey - represents a renewable carbon
source for several fungal fermentations, notably cellulase
production by Hypocrea jecorina (anamorph Trichoderma
reesei), but an effective exploitation of lactose for the
biotechnical utlization is still hampered by its slow
metabolism and a lack of basic knowledge on its utilization
in H. jecorina and filamentous fungi in general. We
therefore have functionally characterized the genes for the
Leloir pathway in H. jecorina. Here we will report that
they differ from the yeast counterparts with respect to
genomic organization, protein structure and genetic
regulation. We will also provide evidence for the
involvement of the Leloir pathway in cellulase induction
by lactose. Further, we will provide evidence for the
existence of a second, so far unknown pathway of Dgalactose
breakdown in H. jecorina and Aspergillus
nidulans which involves a NADPH-aldose reductase
dependent reduction to D-dulcitol, and its subsequent
oxidation by 2-arabinitol dehydrogenase to D-tagatose.