Primary metabolism produces compounds essential for growth like pyruvate and ethanol. Secondary metabolism functions are often unknown and produces specialized compounds in few species after growth stops. Examples of secondary metabolites include antibiotics like penicillin. Secondary metabolites are of interest for industries and their functions include antibiotics, pigments, and toxins. They are classified based on originating from amino acids, shikimic acid, polyketides, or mevalonic acid pathways. Penicillin biosynthesis relies on precursor amino acids from primary metabolism.

2.  Primary metabolism: known function
 Example of primary metabolites:
 Pyruvate
 Ethanol
 Lactic acid
 Primary metabolism is used for:
 Growth and development of hyphal structure
 Energy metabolism
 Regulation of metabolism
 Intermediate in biosynthesis of compound
 Widely distributed in nature

3.  Often lack known function
 Found in few species or genera
 Specialised distribution peculiar to individual species or
small groups of species: idiosynchratic- very
unique, special and specific
 Production of these compounds often after growth has
stopped. Why?
- limitation/nutrients depression
- Contamination- competition
- Fungal cell death due to physical and chemical factors

4. Primary metabolism Secondary metabolism
Function are known Function are usually unknown- lack
Widely distributed in nature Only found in few species or genera -
idiosynchratic
Usually used for growth, energy and as
intermediate
Produced usually after growth has
stopped
Examples: Pyruvate, lactic acid, ethanol Examples:
Penicillin, cephalosporin, gibberellin, lo
vastatin

6.  Some fungi accumulate primary metabolites
 Citric acid
 Fumaric acid
 Ethanol
 Lactic acid

7.  What are the reasons for interest in secondary
metabolites?
 industries:
i. Antibiotic: Penicillin and cephalosporin
ii. Itaconic acid: textile industries
iii. Gibberellin: plant growth regulator
iv. Animal feed
 Pigment
 Bioluminiscences

8.  Mycotoxin
 Aflatoxin: attack crops and cereals, by Fusarium.
 Zearalenone: attack animals (poultry and swine)- cause
infertility and abortion. Can be absorbed by human
skin.
 Phytotoxin and plant growth regulators produced by
pathogenic fungi
 HC toxin: attack Zeamays (maize), from Cochliobolus
carbonum, it is a host specific toxin
 Amatoxin: by Amanita phalloides- A subgroup toxin
 Gibberellin and cytokinins: plant growth regulators

9.  Classified based on 5 main metabolic sources:
1. Amino acid
2. Shikimic acid pathway for biosynthesis of aromatic
amino acid
3. Polyketide biosynthetic pathway from Acetyl CoA
4. Mevalonic pathway from Acetyl CoA
5. Polysaccharides and peptidopolysaccharides
*3 and 4- most involved in production of secondary
metabolites
*amino acid- biosynthetic origins in gycolysis and TCA cycle

10.  Many Ascomycetes and several bacteria
(e.g., Streptomyces) make the β-lactam
antibiotic, Penicillin and Cephalosporin.
 Penicillium chrysogenum, Aspergillus
nidulans, Acremonium chrysogenum
 The precursor substrates for biosynthesis β-lactam are
amino acids
- Show the clear interaction of secondary
with primary metabolites.

11.  Penicillins and cephalopsorins share the initial steps of
their biosynthesis, beginning with Val, Cys and α-
aminoadipic acid.
 These amino acids have their origins in the TCA
 Naturally occurring penicillins produced in the absences of
the side chain precursor supplement in the medium all
contain fatty acid side chains
 Peniciilin F, Penicillin K –derivatives of penicillin with
different side chains

12.  The evolutionary origin of secondary metabolic
pathway comes from sequence comparisons of the
cloned genes
 The genes cloned from Penicillin
chrysogenum, Aspergillus nidulans, Acremonium
chrysogenum
 Revealed in comparison with the analogous genes from
the prokaryotes Streptomyces lipmanii and S.
clavuligerus, striking similarity in both the nucleic
acid and amino acid sequences.

13.  Common evolutionary origin and cross kingdom
transfer of the genes may have occurred about 370 mil
years ago
 P. chrysogenum produces 17 secondary metabolites
 PATULIN- polyketide-related antibiotic produced by
P. Urticae also known as P. Patulum and P.
griseofulvum
 Biosynthesised by acetate malonate pathway

14.  Aspergillus flavus and A. parasiticus
 Carcinogenic properties
 Belong to the polyketide family of secondary
metabolites derived from Acetyl CoA
Aspergillus flavus- stained by
lactophenol blue