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Metabolic
Relationships of Fungi with Oxygen
Majority =
obligate aerobes
Many
=
facultative anerobes
Some
=
obligately fermentative
Few*
=
obligately aneroblic
* Only recently discovered
among animal gut organisms.
Therefore, may be many that yet need
to be discovered.
447
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Major
Respiratory Pathways Associated with
Obligately Aerobic Fungi
1.
Glycolytic/Embden, Meyerhoff, Parnas
(EMP) pathway
2.
Pentose phosphate (PP) pathway
3.
Entner Doudoroff (ED) pathway
4.
Tricarboxylic acid (TCA) or Krebs
cycle pathway*
* Operates in conjunction with
an electron transport chain that dictates
that oxygen acts as the final
electron/hydrogen acceptor.
(see pp. 14 and 15 of handouts)
448b
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Aqualinderella fermentans
1.
[O2]
does not affect amount of lactate produced
2.
[O2]
does not affect amount of glucose consumed
3.
[O2]
does not affect amount fungus grows or at
rate it grows*
*no concentration dependency
of biomass production on [O2*]
as seen with other fungi.
Thus, obligate fermentative
fungus, as Leucosporidium
(Candida) stoffii & RD mutants of S.
cereviseae & N. crassa
453
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Stage
I Events
-
Conversion of C-6 compounds to
appropriate forms and their subsequent
phosphorylation.
a.
ATP requiring step.
Stage II Events
- Degradation
of the phosphorylated C-6 compounds to C3
compounds by various pathways.
a.
These degradation steps can result in
the release of no more than
1/3 of the original
free energy of the hexose.
454
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Stage
III Events -
Degradation of the C-3 compounds to
the C-1 compound CO2
a.
These events (Stage III) bring about
the
formation of numerous
intermediates
which can be used as substrates for
anabolic processes or they can accumulate;
e.g., citric acid.
b.
Release of most of remaining free
energy of the original hexose molecule.
455
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Stage 1 Phosphorylation
Hexokinase*
* Constitutive in yeast &
probably other (all?) fungi having enzyme - S.
cereviseae 2 isoenzymes
* Specificity low = will
phosphorylate D-fructose, 5-beta-D-fructose,
2 deoxy-D-glucose, mannose, D-glucosamine
456a
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Primary Accumulated Metabolism
("overflow
metabolism")
Caused by
metabolic lesions (disruptions in normal
enzyme system caused by mutation or abnormal
growing conditions with strain having
selected enzymes)
stressed
enzyme
A
B
C
D
(low Km)
trapped inside of
C overflow
cell or released
into medium
*examples ethanol, citric acid, phenylalanine, etc., etc., etc.
470
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Conditions for Citrate
Production
1.
high glucose (15 - 20%)
2.
low pH (
2- 4.5)
3.
high aeration
4.
NH4 NO3 [ ] of 2-2.5 g/l
Main
agent of production*
Aspergillus niger
world
wide 1978
175,000 tons/year
*see
handout p. 30
471
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Secondary
Metabolites*
("shunt
metabolites")
Compounds
produced by microorganisms having no known
function in cells and little or no known
economy for cells.
* Production often has little
or no taxonomic relevance
Examples:
penicillins, cephalosporins,
cytochalasins, aflatoxins, griseofulvin,
etc.
472
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Why
20
Metabolites Arise?
1.
Biochemical pathway lesions
2.
Biosynthesis of waste products
3.
Biosynthesis of detoxifying agents
from deleterious products
4.
Biosynthesis of compounds, which are
products of chance events
5.
Biosynthesis of regulators produced
in excess
6.
Biosynthesis of unusual compounds
produced in excess, which are important in
development
7.
Virus or plasmid-mediated products of
metabolism
473
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Tropophase
1.
The exhaustion of an essential
nutrient which leads to the termination or
near termination of cellular proliferation
(balanced phase)
Idiophase
2.
The accumulation of primary
intermediates of metabolism (storage phase)
3.
The triggering of the induction of
enzymes necessary for secondary biosynthesis
by these intermediates, or the
activation of enzymes formed during
tropophase, which lead to product formation
(maintenance phase)
475
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Types
of Fungal Culture Media
1.
Natural - medium represents
essentially unmodified plant or animal
material
a.
complete - seeds, fruit, twigs,
vegetable slices, pollen, dung, hair,
exoskeleton, etc.
b.
partially processed - malt or yeast
extract, potato extract, tomato juice,
cornmeal, peptone, corn steep.
2.
Semisynthetic - media with mixtures
of
partially processed plant &/or
animal products & known pure chemicals
-
e.g., YPG, CMDP, Subaurauds, etc.
3.
Synthetic - media with all
ingredients chemically defined - e.g.,
Vogals synthetic, Westegard's synthetic
cross,
Czapeks Dox, etc.
480
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