Book of Abstracts (PDF) - International Mycological Association

IMC7 Main Congress Theme V: CELL BIOLOGY AND PHYSIOLOGY Posters
strains. Relative as well as absolute amounts of
phospholipids and glycolipids were 1.3 and 4.9 times
higher in mutants with regulatory subunit deleted than in
the control strain. Differences in individual phospholipids
were most distinctive. Mutant strains with increased pkaC
and disrupted pkaR genes showed several times lower
amount of phosphatidylcholine with concomitant increase
in phosphatidylethanolamine and
lysophosphatidylethanolamine, as well as differences in
phospatidylinositol in relation to other followed strains.
Therefore consequences of mutations of PKA on
phospholipid synthesis could be interpreted through cAMP
signaling.
1125 - Copper ions might have a significant role in
redirecting metabolic fluxes in Aspergillus niger
K. Jernejc & M. Legisa *
National Institute of Chemistry, Hajdrihova 19, SI-1001,
Ljubljana, Slovenia. - E-mail: matic.legisa@ki.si
In commercially important micro-organisms, such as
Aspergillus niger, lipid synthesis was often regarded as an
unwanted process since it diverts metabolic fluxes from
final bio-product synthesis - citric acid. The presence of
copper ions was found to induce the citric acid overflow,
while concomitantly lower levels of total lipids were
detected in the cells. Its effect was more obvious in the
medium with magnesium ions as a sole divalent metal ions,
while in the substrate with magnesium and manganese the
addition of copper had less pronounced effect. Since the
malic enzyme was recognised as a supplier of reducing
power in the form of NADPH for lipid bio-synthesis, its
kinetic parameters in regard to different concentrations of
copper ions were investigated and a strong competitive
inhibition of enzyme by Cu2+ ions proposed. It seemed
that copper ions compete with Mg2+ and Mn2+ ions for
the same binding site on the protein, since the deactivation
of malic enzyme after the addition of metal ions was a time
dependent process. Sesamol, another substance reported to
reduce the lipid content in some fungi, had no significant
effect in A. niger cells. The data illustrated that copper ions
were capable of inhibiting the A. niger malic enzyme,
which might lead to redirection of metabolic fluxes from
lipid synthesis toward citric acid overflow.
1126 - Ammonium assimilating GS/GOGAT genes of
the ectomycorrhizal basidiomycete Suillus bovinus
S. Jokela 1* , L. Paulin 2 , R. Sen 1 & J.T. Juuti 1
1
Department of Biosciences, PL 56 (Viikinkaari 9), 00014
2
University of Helsinki, Finland. - Institute of
Biotechnology, PL 56 (Viikinkaari 9), 00014 University of
Helsinki, Finland. - E-mail: sanna.jokela@helsinki.fi
Nitrogen is a major plant growth limiting nutrient in boreal
forests where the bulk of soil nitrogen is bound as organic
complexes inaccessible to uptake by plants. Root symbiotic
ectomycorrhizal fungi are able to mineralize organic soil
nitrogen to ammonium and subsequently translocate
nitrogen as amino acids to mycorrhizal roots. Glutamine
synthetase (GS) and gluamate synthase (GOGAT) are key
enzymes responsible for ammonium incorporation into host
plant and fungal cellular amino acid pools. Genomic and
cDNA libraries were constructed for the ectomycorrhizal
basidiomycete Suillus bovinus, which is commonly found
in Scots pine forest soils. Full genomic GS and GOGAT
sequences, several GS cDNAs and one GOGAT cDNA
were isolated and sequenced. The complete GOGAT
cDNA sequence was determined using RT-PCR.
Transcription initiation sites were identified using primer
extension and confirmed by utilising 5'-RACE methods.
Fungal transcription levels in the Scots pine
mycorrhizosphere were assessed by Northern analysis.
Although present as single copy genes, the amount of GS
transcripts was much higher than that of GOGAT. The
majority of GS transcripts seemed to be non-translatable,
due to loss of mRNA 5'-ends, making the actual amounts of
functional GS and GOGAT transcripts comparable. Total
fungal GS transcript levels seem to be high throughout the
mycorrhizosphere.
1127 - Surface structure and composition of Aspergillus
nidulans walls
S. Kaminskyj 1* , K. Gough 2 & T. Dahms 3
1 Biology Dept. Univ Saskatchewan, Saskatoon SK S7N
5E2, Canada. - 2 Dept. Chemistry, Univ Manitoba,
Winnipeg MB R3T 2N2, Canada. - 3 Dept. Chemistry, Univ
Regina, Regina SK S4S 0A2, Canada. - E-mail:
Susan.Kaminskyj@usask.ca
Wildtype Aspergillus nidulans has highly polarized growth
producing narrow tubular hyphae, but at 42 °C the
conditional non-lethal hypA1 mutation leads to nonpolarized
growth producing wide, tapered cells. TEM
shows that 42 °C hypA1 tip walls are four-fold thicker than
those produced at 28 °C, with wall thickness increasing
subapically. Subapical walls of wildtype hyphae are
inextensible, however, the 42 °C; hypA1 growth pattern
implies they can remain plastic, consistent with Bartnicki-
Garcia's model that wall softening is an integral part of
deposition. Can differences between 28 °C and 42 °C walls
of hypA1 strains be detected at the surface? hypA1 colonies
were prepared for cryo-SEM after growth at 28 °C, 42 °C
or a shift from 42 °C to 28 °C. Surprisingly, the wall
surface was similar for all growth regimes: a finely pebbled
texture, and no evidence of stretching or insertion of
material even at tips. Atomic force microscopy (AFM) can
create a detailed surface image, and in some modes can
also provide chemical information, potentially monitoring
changes as a hypha grows past a fixed point. Here we show
that AFM images reveal the same wall textures in fixed
chemically hypA1 cells as are seen with cryo-SEM.
Nevertheless, despite the similarity between these surface
images, infrared spectroscopy of wildtype hyphae showed
that tips were relatively enriched for protein compared to
subapical regions, which were enriched for carbohydrate.
Book of Abstracts 341