Secondary metabolism
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Transcript of Secondary metabolism
Secondary Metabolism
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
Primary Metabolites
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
Secondary Metabolites
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,
lovastatin
Differences between primary metabolism and secondary metabolism
Common metabolites generated from secondary biosynthesis pathways in fungi
Some fungi accumulate primary metabolites
Citric acidFumaric acidEthanolLactic acid
What are the reasons for interest in secondary metabolites?
industries: i. Antibiotic: Penicillin and cephalosporinii. Itaconic acid: textile industriesiii. Gibberellin: plant growth regulatoriv. Animal feed
Pigment Bioluminiscences
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
Toxic Metabolites by Fungi
Classified based on 5 main metabolic sources:
1. Amino acid2. Shikimic acid pathway for biosynthesis of aromatic
amino acid3. Polyketide biosynthetic pathway from Acetyl CoA4. Mevalonic pathway from Acetyl CoA5. Polysaccharides and peptidopolysaccharides
*3 and 4- most involved in production of secondary metabolites
*amino acid- biosynthetic origins in gycolysis and TCA cycle
Biosynthesis of secondary metabolites
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.
β-Lactam antibiotic
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
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.
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
Aspergillus flavus and A. parasiticus
Carcinogenic properties
Belong to the polyketide family of secondary metabolites derived from Acetyl CoA
Aflatoxin
Aspergillus flavus- stained by lactophenol blue