CHEMICAL REQUIREMENTFOR GROWTH

GROWTH

the tendency of organisms to increase in size, mass and parts is a complex process

Most commonly used measures ofgrowth are dry weight and colony diameter.

Basic growth tendency is exponential, but may be modified by physical and chemical limitations.

Hyphal elongation and growth of a singleyeast cell are linear

Branching cell division create new growing points

All of these – chemical limitation –disrupt

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?

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.

Nutritional requirements

C, N & S sources, vitamins and growth factors

O2, CO2, H2O, H+ = ?

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

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.

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.

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

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.

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.

Cobalt - not essential directly but some fungus are auxotrophic for vitamin B12.

Some marine fungus – Na as a macronutrient – replaces K –some functions

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

Glucose Found in cellulose, starch and other CHO Benefits:1. Able to utilize fully2. No adaptation period3. Good for initiating a study with no

nutritional information available

Fructose and mannose are the next most commonly utilized sugars, galactose.

1. Need adaptation period2. Initiated by low conc. Glucose3. Induce mannose-utilizing enzymes What about growth on disaccharides,

oligosaccharides and polysaccharides?

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.

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.

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

Other Chemical factors

Carbon dioxide Oxygen Water Hydrogen ion

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.

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.

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.