1. CHEMICAL
REQUIREMENT
FOR GROWTH

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.

6. Nutritional requirements
 C, N & S sources, vitamins and growth factors
 O2, CO2, H2O, H+ = ?

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.

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

22. Other Chemical factors
 Carbon dioxide
 Oxygen
 Water
 Hydrogen ion

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.