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mycology lecture 7 Fungal nutrition, metabolism

mycology lecture 7 Fungal nutrition, metabolism

What is required for the growth of fungi?

Slightly acidic conditions ph<5 and rich in carbohydrates. In bacteria a neutral or slightly basic pH is needed and rich in nitrogen

Some fungi require vitamins for growth, which vitamins?

Biotin and thiamine

With the vitamins biotin and thiamine fungi can produce what?

Fungi can then produce all the essential amino acids

What do fungi need for the amino acid formation?

Organic nitrogen. Some cant handle ammonium or nitrate.

Where do they get the nitrogen?

They get it from the amino acid, asparagine. Basidiomycota do this.

What do oomycota require for reproductive phase?

Sterols, and need the amino acid cysteine for S, cuz they cant use organic S

What do zygomycota need for nutrition?

They need animal dung fungi, iron(heme group) for cytochromes in respiratory pathway

For chytridiomycota: Saccharomyces

aerobic conditions are ok but under anaerobic conditions, different pathways will be used.

Some fungi can use carbon sources not miscible in water(live in water/hydrocarbon surface). What are they?

-Methane, methanol, formaldehyde, F6P

-Long chained carbon compounds: C9 or longer

What are aviation kerosine?

Clog filters, and corrodes walls of storage tanks

What do the vast majority of fungi use as energy sources?

Glucose, monosaccharides, disaccharides, some aminosugars, sugar acids, sugar alcohols

What does the energy source used by fungi depend on?

Depends on the presence of transport membrane proteins.

What do most fungi have a transport preference for?


What is the problem with having glucose as a presense?

Because the fungi have a low binding specificity for glucose

What happens when other sugars are utilized?

Can induce the transport proteins required

For example:Lactose degraded to galactose and glucose

-Fungus slurps up glucose

-When glucose runs out, growth rate slows -Transport protein pathway generated for galactose

-Galactose uptake starts

-Growth rate increases

When we use polymers for energy sources specific enzymes are required.

What enzymes are needed for starch?


What enzymes are needed for lipids?


What enzymes are needed for proteins?



To summarize: Fungi exploit a wide variety of organic sources

In all cases, nutrients must be in soluble, simple form

Nutrients must diffuse through the wall and enter cells via membrane transport proteinsAllow only: monosaccharides, amino acids, and peptides of three or fewer amino acids

Larger molecules: degraded by extracellular enzymes (depolymerases) secreted by the fungi


How do fungi capture nutrients?

By an electrical current created by a proton pump

What is the charge at the tip?

More electronegative at tip than further back

What is the current carried by?


Can the electrical current be reversed?


Does the electric current affect the growth of the hyphal tip?

No, therefore it has nothing to do with growth rates directy.

What happens during the nutrient uptake process?

Energy is being expended

Where is the energy being extracted from?

Dissociation of ATP

What are symporters?

transport proteins where ion's re-enter

Where are the symport transport proteins located?

Located close to the tip

Where do the ion pumps located?

Farther back from the apex near the mitochondria.

What do the ion pumps do?>

Supply ATP needed for protein pumps

What creates the electrical current?

spatial separation

Rate if diffusion of large molecules limit the fungal growth. Enzymes are large molecules. Rate of diffusion of soluble molecules to hyphal tip would be too slow.

Fungi create zones of 'nutrient erosion'. They release digestive enzymes that create a zone of substrate erosion. This area is now devoid of nutrients.

How do enzymes escape the hyphae if the enzymes are so big that they cant squeeze out from the pores on the hyphae?

They pour our at the hyphal tip at areas of new growth, exocytosis, flow out with wall components, some are destined to flow out into the environment, some locked into wall.

Fungi will defend acquired nutrients. Rate of enzyme production matches closely with amount of breakdown of products. Final stages of polymer breakdown are done by wall enzymes. Keeps the monomers close to the hyphae; away from other organisms. Antibiotics are released near areas of soluble monomers. Antibiotics produced mainly by polymer degrading fungi.


What is the most abundant polymer on earth?

Cellulose(=40% of all plant biomass on earth)

What is cellulose?

Simple polymer consisting of 2000-14000 glucose residues.

Each glucose is rotated 180degrees to the one next to it. Every two residues represents a repeating pair. Easy for enzymes to attack and degrade.


Cellulose chains are stacked together in crystalline-like form called a micelles which is reinforced by hydrogen-bonding. Micelles are aligned into microfibrils of 10nm in diameter. These rigid microfibrils are very insoluble and hard to attack by enzymes.


How many enzymes does it take to break down cellulose?

three enzymes.

What are the enzymes collectively called?

cellulase enzyme complex

What are the three enzymes and what do they do?

endoglucanase: breaks cellulose chains into fragments

cellobiohydrolase: works on cellulose ends into disaccharide cellobiose units

B-glucosidase: cleaves disaccharide cellobiose to glucose

All three act synergistically to degrade celluloseEndoglucanase creates more and more ends for cellobiohydrolase to attack.Cellobiohydrolase creates more and more cellobiose Can bind to active site of cellobiohydrolase as accumulates (competitive inhibition)Links rate of breakdown of cellobiose to rate of use of glucose by fungus


As more glucose becomes available, it causes gene repression of genes encoding for production of enzymes, what is this called

Catabolite repression

What does this process closely regulate process for?

Cellulose breakdown

In the absense of glucose what happens?

Gene induction occurs and production of enzyme increases.

What are some significant nutrients needed by fungi?

Nitrogen, phosphorous and Iron

What is the most required nutrient and why?

Nitrogen, because fungi cant fix atmospheric nitrogen. Instead they obtain it from amino acids and nucleotides.

What is the normal pathway for assimilation of nitrogen?


>can produce all essential amino acids

Many fungi can use nitrate for the Nitrogen source. Some water moulds can not utilize ammonia or ammonium. Most utilize organic sources of N


What is phosphorous needed for?

nucleic acids, ATP, membrane phospholipids

Why is it hard to obtain?

Low amounts in natural environment, usually in insoluble form, plant roots have trouble extracting it from the soil

What does a critically low P in soil trigger fungi to do?

Triggers fungi to activate their Phosphorous uptake system.

What does the system do?

Release phosphatase enzymes into the soil that cleave phosphates from organic sources. It can also solubilize insoluble P by releasing organic acids and lowering external pH.

What does the high surfaace/volume ratio of hyphae do?

Good for uptake and constantly moving into new territory. Accumulate and store excess phosphate. The cost of sugars vs. producing new roots is worth it.

Why is iron needed?

Needed for donor/acceptor molecules in the cytochrome system of respiration, thus only small amounts are needed.

Which form does the iron normally occur in?

Fe3+ ferric form

What pH is iron insoluble in soil at?

5.5 or higher and its in the form of hydroxides or oxides.

What captures the iron to be used?

Chelation, a compound that combines with the iron

What are siderophores?

They are iron-chelating compounds. They capture Fe3+ and then are reabsorbed by fungi through a special membrane pores for the siderophores.

The Fe3+ is reduced to Fe2+ and released. Fe2+ has lower affinity. The siderophores are also released to capture more Fe3+