The main source of carbon and energy in industrial media is carbohydrates. In recent times hydrocarbons have been used. The catabolism of these compounds will be discussed briefly because they supply the carbon skeletons for the synthesis of primary as well as for secondary metabolites.
The inter-relationship between the pathways of primary and the secondary metabolism will also be discussed briefly.
Catabolism of Carbohydrates:

Four pathways for the catabolism of carbohydrates up to pyruvic acid are known. All

four pathways exist in bacteria, actinomycetes and fungi, including yeasts. The four
pathways are the Embden-Meyerhof-Parnas, the Pentose Phosphate Pathways, the
Entner Doudoroff pathway and the Phosphoketolase. Although these pathways are for
the breakdown of glucose. Other carbohydrates easily fit into the cycles.
(i) The Embden-Meyerhof-Parnas (EMP Pathways): The net effect of this pathway is
to reduce glucose to pyruvate . The system can operate under both
aerobic and anaerobic conditions. Under aerobic conditions it usually functions
with the tricarboxylic acid cycle which can oxidize pyruvate to carbon dioxide and water.
Under anaerobic conditions, pyruvate is fermented to a wide range of fermentation
products, many of which are of industrial importance.

The pentose Phosphate Pathway (PP): This is also known as the Hexose
Monophosphate Pathway (HMP) or the phosphogluconate pathway. While the
EMPpathway provides pyruvate, a C3 compound, as its end product, there is no
end product in the PP pathway. Instead it provides a pool of triose (C3), pentose (C5), hexoses(C6) and heptose (C7) phosphates. The primary purpose of the PP
pathway, however, appears to be to generate energy in the form  of NADPA2 biosynthetic and other purposes and pentose phosphates for nucleotide synthesis.

The Entner-Doudoroff Pathway (ED): The pathway is restricted to a few bacteria
especially Pseudomonas, but it is also carried out by some fungi. It is used by some

organisms in the anaerobic breakdown of glucose and by others only in gluconate metabolism.
The Phosphoketolase Pathway: In some bacteria glucose fermentation yields lactic
acid, ethanol and carbon dioxide.
 Pentoses are also fermented to lactic acid and acetic acid.

An example is Leuconostoc mesenteroides.

Pathways used by microorganisms
The two major pathways used by microorganisms for carbohydrate metabolism are the
EMP and the PP pathways. Microorganisms differ in respect of their use of the two
pathways. Thus Saccharomyces cerevisiae under aerobic conditions uses mainly the EMP
pathway; under anaerobic conditions only about 30% of glucose is catabolized by this
pathway. In Penicillium chrysogenum, however, about 66% of the glucose is utilized via the
PP pathway. The PP pathway is also used by Acetobacter, the acetic acid bacteria.
Homofermentative bacteria utilize the EMP pathway for glucose breakdown. The ED

pathway is especially used by Pseudomonas.

Cited By Kamal Singh Khadka
Msc Microbiology, TU.
Assistant Professor In PU, Pokhara Bigyan Thata Prabidhi Campus, PNC, NA, LA.
Pokhara, Nepal.


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