Fermentation Products: Physiological and Bioenergetic Considerations
The overproduction of substances by microbial cultures is discussed in a bioenergetic context. Since many fermentation products are generated by energy-yielding reactions, it is clear that the rate of energy consumption of a cell will influence the rate of product formation. It is shown that the nature of the growth environment influences to a great extent the magnitude of these energy-consuming reactions. On the other hand, the energetic efficiency of the energy-generating reactions can be reduced and this will lead, assuming the same rate of energy consumption, to an increased rate of product formation. Another class of products, in particular proteins, can only be produced by energy-consuming reactions. Therefore, the extra energy consumption caused by the overproduction of proteins is in direct competition with the energy consumption that the cell requires for maintenance and growth. The physiological implications of this metabolic conflict are discussed and it is suggested that this type of overproduction will be inherently unstable, unless the overproduction of a protein increases the fitness of the producer organism.
KeywordsFermentation Product Chemostat Culture Paracoccus Denitrificans Producer Organism Maintenance Energy Requirement
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