Characteristics of secondary metabolites:
a. Secondary metabolites were specifically produced by selected microorganisms.
b. Secondary metabolites were less essential for development and reproduction
of organisms.
c. Environmental factors were influenced the production of secondary metabolites
(Pal et al. 2019b).
d. Certain microorganisms can produce structurally related secondary
metabolites as a group of compounds not a single one such as anthracyclines,
produced by Streptomyces.
e. The biosynthetic pathways of were not clearly established for most secondary
metabolites.
f. The regulation of the formation of secondary metabolites was more complex
than primary metabolites (Pal et al. 2018).
Functions of secondary metabolites: There were two possible hypotheses for the
justification of secondary metabolite function as:
a. Secondary metabolites were beneficial for the cells to survive.
b. The secondary metabolites were important for the cell development.
The metabolic regulation was equally complex to achieve overproduction of
secondary metabolites. Some regulatory mechanisms were as follows:
i. Induction: Methionine addition induced certain enzymes, which enhanced
the production of cephalosporin. Also tryptophan regulated ergot alkaloid
biosynthesis.
ii. ii. End product regulation: Secondary metabolites inhibited their own
biosynthesis by negative feed regulation such as penicillin, streptomycin,
puromycin and chloramphenicol (Pal et al. 2019c).
iii. Catabolite regulation: In this process, a key enzyme was participated in the
catabolic pathway was inactivated, inhibited or repressed the process.
Catabolic repression was obtained by carbon or nitrogen sources. Where
the most common source of carbon was glucose, which was participated in
the inhibition process of several antibiotics, such as: penicillin, streptomycin, bacitracin, chloramphenicol, puromycin; whereas ammonia was the
primary source of nitrogen which was catabolite regulators for the overproduction of certain antibiotics (Pal et al. 2019d).
iv. Phosphate regulation: Inorganic phosphate was essential for the growth and
multiplication of prokaryotes and eukaryotes. Concentration of inorganic
phosphate (up to 1 mM) was directly correlated with the concentration of
secondary metabolites e.g. streptomycin, tetracycline, alkaloids, gibberellins.
v. Auto regulation: Certain microorganisms such as: actinomycetes were
associated with the self-regulation for the production of secondary
metabolites. A compound (factor A) was a derivative of a hormone was
suggested to be closely involved in auto regulation for the production
streptomycin by Streptomyces griseus.
4
S. Saha and D. Pal
a. Secondary metabolites were specifically produced by selected microorganisms.
b. Secondary metabolites were less essential for development and reproduction
of organisms.
c. Environmental factors were influenced the production of secondary metabolites
(Pal et al. 2019b).
d. Certain microorganisms can produce structurally related secondary
metabolites as a group of compounds not a single one such as anthracyclines,
produced by Streptomyces.
e. The biosynthetic pathways of were not clearly established for most secondary
metabolites.
f. The regulation of the formation of secondary metabolites was more complex
than primary metabolites (Pal et al. 2018).
Functions of secondary metabolites: There were two possible hypotheses for the
justification of secondary metabolite function as:
a. Secondary metabolites were beneficial for the cells to survive.
b. The secondary metabolites were important for the cell development.
The metabolic regulation was equally complex to achieve overproduction of
secondary metabolites. Some regulatory mechanisms were as follows:
i. Induction: Methionine addition induced certain enzymes, which enhanced
the production of cephalosporin. Also tryptophan regulated ergot alkaloid
biosynthesis.
ii. ii. End product regulation: Secondary metabolites inhibited their own
biosynthesis by negative feed regulation such as penicillin, streptomycin,
puromycin and chloramphenicol (Pal et al. 2019c).
iii. Catabolite regulation: In this process, a key enzyme was participated in the
catabolic pathway was inactivated, inhibited or repressed the process.
Catabolic repression was obtained by carbon or nitrogen sources. Where
the most common source of carbon was glucose, which was participated in
the inhibition process of several antibiotics, such as: penicillin, streptomycin, bacitracin, chloramphenicol, puromycin; whereas ammonia was the
primary source of nitrogen which was catabolite regulators for the overproduction of certain antibiotics (Pal et al. 2019d).
iv. Phosphate regulation: Inorganic phosphate was essential for the growth and
multiplication of prokaryotes and eukaryotes. Concentration of inorganic
phosphate (up to 1 mM) was directly correlated with the concentration of
secondary metabolites e.g. streptomycin, tetracycline, alkaloids, gibberellins.
v. Auto regulation: Certain microorganisms such as: actinomycetes were
associated with the self-regulation for the production of secondary
metabolites. A compound (factor A) was a derivative of a hormone was
suggested to be closely involved in auto regulation for the production
streptomycin by Streptomyces griseus.
4
S. Saha and D. Pal