Some investigations concerning the entropy balances of microbial fermentations — primary and secondary metabolite production
✍ Scribed by Dr. E.-J. Bormann; H. H. Grosse; J. Menz
- Publisher
- John Wiley and Sons
- Year
- 1988
- Tongue
- English
- Weight
- 425 KB
- Volume
- 28
- Category
- Article
- ISSN
- 0233-111X
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✦ Synopsis
In order to check the usefulness of the resulting equations of a model concerning entropy balances. of microbial fermentation processes apropriate experiments were analyzed. To take into account both primary and secondary metabolism data of previously carried out fermentations of the amino acid L-lysine and the antibiotic nourseothricin respectively were used.
The obtained results indicate the agreement of the calculated values with the supposed thermodynamic relations showing the expected decrease of entropy production to a minimum as well as the zero balance of the entropy variation.
The course of entropy production during the phase of product formation gave rise to discuss this phenomenon from a more general viewpoint with respect to the role of secondary metabolites as a possible way to avoid "overheating" of cells or membranes although energy substrates are available in excess.
Although no final solution has been achieved up to now with respect to the discussion as to wether the thermodynamics of irreversible processes is also applicable for biological systems (TRINTSCHER 1976, BERTALANFFY et aE. 1977, WILSON 1982), a number of publications have supposed the validity of the basic equation of entropy variation (PRIGOGINE 1962) for living organism. The application of this theory allows entropy production to be determined by the measurement of the entropy transfer, expressed as the rate of heat production, whereby steady state conditions must be provided, i.e. logarithmic growth or continuous cultivation, to ensure the equality (with negative signature of entropy transfer) of the two quantities.
Recently BERMUDEZ and WAGENSBERG (1986) published a set of equations to study entropy balances during the period of microbial growth. They estimated the phenomenological coefficient L (compare GLOMBITZA et al. 1984) since this describes the coupling of metabolic fluxes, represented by the growth rate, to the metabolic forces, which are defined in the model in terms of microbial affinities.
In accordance with GLOMBITZA and HEINRITZ (1979) the results obtained demonstrated the validity of thermodynamic suppositions, because the entropy variation was decreased near zero, whereas the entropy production fell to a minimum. However, the argument, that along with the microbial growth rate the non growth-associated product formation as well as the maintenance metabolism also both maintained certain steady state values, made it worthwhile to include both these metabolic phenomena in investigations of entropy balance in microbila fermentations.
Therefore, the equations of substrate consumption and product formation gained from the model of BERMUDEZ and WAGENSBERG (1986) were modified. Appropriate statements according to LUONG and VOLESKY (1984) were used in a slightly modified form, according to BORMANN (1986), together with the maintenance concept of PIRT (1982).