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Title: Maintenance energy and molar growth yields of Escherichia coli
Author: Wallace, Robert John
ISNI:       0000 0001 3557 3827
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1975
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Maintenance is that fraction of the metabolic activity of growing cells which does not result in the net synthesis of new cell material. The maintenance coefficient (m) is assumed to be constant, and independent of specific growth rate (mu). It can be measured by, examining the distribution of carbon to new cells and to energy production at various mu. In the arithmetic growth systems employed in this work mu changes in a predictable way and at the slow growth rates attained (mu = 0.01 - 0.1 h-1) m is a large fraction of the total energy utilisation. These factors made more simple the accurate measurement of m in comparison with methods employed by other workers. Both the maximum molar growth yield (YG) and m were readily measured using arithmetic-type continuous culture. Value of YG and YGO2 were similar to those obtained by other workers using different growth systems. The main conclusions were (i) anabolic and catabolic processes in carbon-limited were tightly coupled, but coupling broke down under nitrogen limitation; (ii) using the Bauchop and Elsden YATP of 10.5 g/mole, P/0 ratios for carbon-limited E. coli were 2 for growth on glucose, malate and glycerol, and 3 for growth on lactose. Addition of 0.5 M sodium chloride to a glycerol-limited culture reduced the P/0 ratio to 1. These P/0 ratios seemed reasonable, implying that the previous assumption of the value for YATP was probably valid, and hence YATP was considerably less than the theoretical maximum of ~30 g/mole. Maintenance in terms of carbon source and oxygen was measured in the same experiments. Findings were (i) carbon source used for maintenance was completely oxidised; (ii) maintenance energy is small in E. coli. mATP was 1 - 3 mmol (g dry wt)-1 h-1 at 37°; (iii) at least two components make up the maintenance requirement. One is relatively constant with respect to carbon source and temperature, and the other has a very high temperature coefficient, which is characteristic of the particular carbon source used; (iv) part of the maintenance requirement may be an osmotic effect. Addition of 0.5 M sodium chloride to a glucoselimited culture at 37° increased m by 44%; (v) maintenance of the structural organisation of the respiratory apparatus may require energy. The maintenance coefficient of a glycerol-limited culture fell when the P/0 ratio decreased; (vi) m from glycerol-limited chemostat culture was 3x the value of m obtained from glycerol-limited arithmetictype continuous culture. It was postulated that m may not be constant for all y, although it may appear to be constant from measurements made over small ranges of y. Turnover of enzymes, protein, cell walls and total cell phosphate and carbon were measured in arithmetic-type continuous culture to identify any turnover reactions which may have a similar temperature coefficient to maintenance. The Arrhenius activation energy of each of these processes was an order of magnitude less than that of the component of maintenance with the high temperature coefficient. However, turnover of macromolecules was not eliminated as a possibility for the maintenance coefficient which remains constant below 30°. The large Arrhenius activation energy of maintenance is of the same order as denaturation. Protein turnover data showed that this component could not be the replacement of denatured protein de novo. It is more likely that it is caused by the disruption and subsequent repair or re-assembly of cell structure, particularly of multienzyme complexes, ribosomes and membrane components.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available