2. GROWTH
the tendency of organisms to increase in size,
mass and parts is a complex process
Most commonly used measures of
growth are dry weight and colony diameter.
Basic growth tendency is exponential, but may
be modified by physical
and chemical limitations.
3. Hyphal elongation and growth of a single
yeast cell are linear
Branching cell division create new growing
points
All of these – chemical limitation –disrupt
4. What Do Fungi Do?
Degrade compounds
Recycling C, N, S as nutrients for growth of
other organisms
Cause deterioration of materials
Breaking down and detoxifying wastes and
other pollutants
Therefore, to cultivate fungi in the lab, what do
you must know?
5. Chemical Requirements
2 Categories:
Nutrients incorporated into the substance of
the fungus
Chemical factors necessary for a salubrious
environment but are not used as part of the
substance of the fungus.
7. In mineral nutrition studies, a major problem is
to:
provide a medium that is free of an element
show a response to graded amounts of it
Easy for macronutrients but often difficult for
micronutrients- O2, Cu, Mn, Zn, Fe
Show inhibitory effect if excess
8. Interactions between nutrients eg. the sparing
effect of Na on the K requirement of
Aspergillus, may interfere with the
interpretation of data.
Addition of NaCl reduced the amount of KCl
required for optimum growth.
Such data do not necessarily indicate the
utilization of sodium by the fungus
May be reflect the release of K ion from
nonspecific binding.
9.
10.
11. However, Na may have a functional role as
indicated for the marine fungus
Thraustochytrium roseum (Belsky et al., 1970)
Sodium is required for phosphate transport by
this fungus - cannot be replaced by other
monovalent cations.
12. Appropriate controls are essential to any
experiment.
Amino acids used as the source of N or sulfur
also provide C.
So, what do you have to do?
Include a control lacking the tested C source
13. Negative results – difficult to interpret
Do not necessarily show that the fungus is
incapable of using the substance in question.
Adverse changes
Incomplete knowledge of the nutrition of the
fungus may lead to problems with
contaminating vitamins.
14. Essential Elements
Macronutrients: C, H, O, P, K, N, S and Mg
Required at about 10-3M
Micronutrients
Required at about 10-6M or less
Essential mineral elements - accepted
Other elements : Sc, V and Ga.
15. Cobalt - not essential directly but some fungus
are auxotrophic for vitamin B12.
Some marine fungus – Na as a macronutrient
– replaces K –some functions
16. Carbon Nutrition
Entire spectrum of compounds as sources of C
and E.
Ability to use these compounds depends on:
1. Digestion of oligomeric and polymeric
materials
2. Transport of the monomers through
plasmalemma
3. Phosophorylation of CHO or
gluconeogenesis
17. Glucose
Found in cellulose, starch and other CHO
Benefits:
1. Able to utilize fully
2. No adaptation period
3. Good for initiating a study with no nutritional
information available
18. Fructose and mannose are the next most
commonly utilized sugars, galactose.
1. Need adaptation period
2. Initiated by low conc. Glucose
3. Induce mannose-utilizing enzymes
What about growth on disaccharides,
oligosaccharides and polysaccharides?
19. Many C sources are heat-stabile
Significantly altered by reaction with other
ingredients of medium
Sucrose – hydrolized at slightly acid pH.
Ability of the fungus to use a compound as a
sole source of C may differ from its ability to
use it as a C source in combination with other
substrates.
20. Nitrogen and Sulfur
N & S function in fungus in the reduced state
in organic combination as amino nitrogen and
sulfhydril sulfur, but utilized as oxidized
inorganic ions.
NH4 –widely utilized.
Urea, amino acids and other organic N – less
Nitrogen fixation by fungi ?
Only members of Saproleginiales and
Blastocladiales cannot utilize sulfate as source
of S.
21. Growth Factors
VITAMINS
Fungi have natural deficiencies for vitamins that
are satisfied at μM to nM concentrations.
STEROLS
Enhanced growth and sporangium production with
such sterols as cholesterol, cholestanol, sitosterol
and stigmasterol
OTHER GROWTH FACTOR
Flavonoids
Taxifolin glucoside
23. Chemotropism and Chemotaxis
Chemotropism, the ability to grow towards
Chemotaxis, the ability to migrate towards an
attractant
Chemotaxis and chemotropism require the
ability to detect a signal, transmit this signal
intracellularly and respond to the signal by
oriented movement and growth.
24. For effective response, cells must be able to
detect small differences in attractant
concentration, and detection must convey
directional information to the cell.
In many instances, it is necessary that cells be
able to detect and respond rapidly to subtle
differences in attractant concentration.
A response to an external signal must override
or reprogram default cellular growth
processes.
25. Chemotaxis was observed under the
microscope of the swimming behaviour of
zoospores in relation to a source of attractant
and by observation of the massing spores on
root surfaces.