Microbial Products

Most of the natural products constituted by carbon, nitrogen, hydrogen, oxygen and phosphorus can be fermented under anaerobic conditions by microorganisms. There are many fermentation products used commercially (Fig. 14.6). A list of some microorganisms and their products are given in Table 14.1.

Primary Metabolites
After inoculation when microbial growth is in exponential or trophophase many intermediate metabolic products are produced. These are further needed either in growth (e.g. amino acids, nucleotides, proteins, carbohydrates, lipids, vitamins, etc), or energy yielding catabolism (e.g. acetone, ethanal, butanol, organic acids, etc). Therefore, the metabolites produced during trophophase are known as 'primary metabolites'. The concentration of some of the metabolites exceeds many times more than required by the producers. The principal primary metabolites and the respective micro-organisms are given in Table 14.1.

Reduction of glucose into some important products during fermentation. 1-yeast; 2-propionibacteria; 3-clostridia; 4-coli-aerogenes groups; 5-lactic acid bacteria (modified after Schlegel, 1986).
Fig. 14.6. Reduction of glucose into some important products during fermentation. 1-yeast; 2-propionibacteria; 3-clostridia; 4-coli-aerogenes groups; 5-lactic acid bacteria (modified after Schlegel, 1986).
Secondary Metabolites
When the trophophase of growing culture is over, then starts the idiophase. Microbial products other than primary metabolites produced during idiophase by slow growing or non-growing cells of microorganisms are known as secondary metabolites or idiolites such as toxins, gibberellins, alkaloids, and antibiotics. The secondary metabolites play no role in growth of microorganisms. It is produced by a limited number of microorganisms (Table 14.1) when depletion of one or more nutrients is caused in culture medium.

Enzymes
Enzymes are naturally occurring biocatalysts which accelerate metabolic reactions. Various metabolic activities and production of primary and secondary metabolites are not possible without the involvement of enzymes. Enzymes produced during fermentation are mostly extracellular but a few are intracellular for example asparaginase, invertase and uric acid. Intracellular enzymes may be produced in industries, but with many difficulties. The important extracellular enzymes are amylases, cellulases, invertase, 6-galactosidase (lactase), esterase, lipases, proteases.

Table 14.1. Microorganisms and their products.
Algae Microbial products
Primary metabolites
(1)
Secondary metabolites
(2)
Enzymes
(3)
Others
(4)
Chlorella sorokiniana - - - SCP
Spirulina maxima - - - SCP
S. platensls - - - SCP

Bacteria Microbial products
Primary metabolites
(1)
Secondary metabolites
(2)
Enzymes
(3)
Others
(4)
Acetobacter aceti Acetic acid - - -
Acetobacterium woodii Acetic acid - - -
Bacillus brevis - Gramicidin - -
B. polymyxa - Polymyxin B Amylase -
B. popilliae - Endotoxin - -
B. subtilis - Bacitracin - -
B. thuringiensis - Endotoxin - -
Clostridium aceticum Acetic acid - - -
Gluconobacter
suboxydans
Vinegar - - -
Meihylophilus
methylotrophus
Glutanic acid - - -
Pseudomonas
denitrificans
Vitamin B12 - - Yoghurt
Actinomycetes : - - - -
Micromonospora
purpurea
- Gentamicin - -
Nocardia mediterranei - Rifamycin - -
Streptomyces
aureofaciens
- Tetracycline - -
S. tradiae - Neomycin - -
S. griseus - Streptomycin - -
S. noursei - Nystatin - -
Fungi : - - - -
Aspergillus niger - Citric acid - -
A. oryzae - - Amylase Cellulase Amylase SCP,
Soya sauce
Candida lipolytica - - Lipase Soya sauce
C. utilis - - - SCP
Cephalosporium
acremonium
- Cephalosporin - -
Fusarium
moniliforme
- - - SCP
Gibberella
fujikuroi
- Gibberellin - -
Morchella esculenta - - - SCP
Penicillium
chrysogenum
- Penicillin - -
Rhizopus arrihizus, - - - -
R. nigricans - Steroides - -
Saccharomyces
cerevisiae
- - - SCP, wine, bakery
S. lipolytica - - - SCP
Trichoderma
harzianum,
T. reesei, T. viride
- - Cellulase -
SCP = Single Cell Protein.

Microbial Biomass
Microbial cells which produce many commercial products, themselves serve as main source of biomass. Microbial biomass is also known as microbial protein or single cell protein (SCP). SCP plays a significant role in supplying the protein in world food shortages. Production of SCP and its application have been described in detail in Single Cell Protein (SCP) and Mycoprotein.

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