FERMENTATION METABOLIC PATHWAYS

We have always looked at fermentation process or the formation of fermentation products by microorganisms as something beneficial to man. While we are deriving the benefits from the activities of the fermentation microorganisms, in reality the action of these microorganisms are really not to serve the human masters but more to their selfish ends. To these microorganisms, the fermentation activities are their mode of survival. Fermentation is their metabolic and physiological method of deriving energy from the substrates for their growth.
The fermentation products during their metabolism are just their metabolic waste products which have served their duty. If however, the human beings get their pleasure by consuming their waste products……well and good for these pathetic humans. Nothing is stopping these humans from drinking their metabolic urine or alcohol !
In fact the cornerstone of human civilization in history has always depend on these fermentation products. There is a rich diversity of fermentat ion products as reflected in the culture of various countries. In essence, the diversity is quite limited in terms of the microorganisms and metabolism involved. The fermentation products are just given different brand names in different languages and by the use of different substrates found in the specific countries
The fermentative microorganisms metabolize the substrate to extract their enegy. This is executed by various metabolic pathways found in the microorganisms. It should be stressed that there is a diversity of metabolic pathways available, depending on the type of microorganisms, substrates and physiological environment. What is important to note are:
1 There are a number of fermentation pathways available in a microorganism
2 TCA cycle is only available in aerobic microorganism, BUT at the same time these aerobic microorganisms too have anaerobic or fermentation pathways . These microorganisms too are carrying fermentation process in their metabolism
Most students, in their early stages of learning microbial metabolism erroneously tend to think that only one or two pathways are involved. Or they only tend to think that in the study of fermentation metabolism only carbohydrate catabolism is important! Nothing could be further than truth in these assumptions. It is like saying lipids and proteins are not used as substrates in fermentation.
The beauty about having many fermentation pathways interlinking allows the fermentation microorganisms adaptability in the uncertain environment....and their survival!!!
The changing of tracks in metabolic pathways are achieved by the presence of branch end compounds. Branch compounds are compounds which interlinked two or more metabolic pathways. On reaching a branch end compound the microorganism will have the choice to go for one or other pathway depending on the circumstances. A very central branch end compound is pyruvate. From pyruvate the metabolism can go almost any where.
Such branch end compound such as pyruvate allows the effective linking of carbohydrate, lipid and protein metabolism. It also linked the various anabolic, catabolic and intermediary metabolism.


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