| Summary: | The energetics of Escherichia coli W, growing aerobically in carbon-, oxygen-, ammonium-and sulphate-limited continuous cultures were investigated. Room temperature difference spectra of respiratory membranes prepared from the cultures revealed the presence of cytochrome b and cytochrome oxidase o. In addition, cytochromes a1 and d were present in oxygen-limited cultures. Endogenous?H+/o quotients of whole cells from all of the cultures were consistent with the presence of respiratory chains with two proton translocating segments between NADH and oxygen. Glycerol-limited cultures at 30.0°C yielded Yomax2 (the maximum molar growth yield with respect to oxygen) and Ymaxatp (the maximum molar growth yield with respect to ATP equivalents) values of 50.9 g cells.mole 02-1 and 12.7 g cells.mole ATP equivalents respectively, together with a value for M (the energy requirement for maintenance purposes) of 2.32 mmole ATP equivalents.h-1.g cells-1. When the temperature of growth was decreased to 20.3°C, YmaxATP remained relatively unchanged at 11.7 g cells.mole ATP equivalents-1 but M decreased to 0.4 mmole ATP equivalents. h-1. g cells-1. Increasing the temperature of growth to 42.3°C caused YmaxATP to decrease to 7.6 g cells.mole ATP equivalents-1 and M to increase to 7.4 mmole ATP equivalents.h-1.g cells-1. Replacement of glycerol by other limiting carbon substrates caused YmaxATP and M to alter within the range 7.1 (acetate) to 13.9 (glucose) g cells.mole ATP equivalents-1 and 1.9 (glucose) to 6.7 (malate) mmole ATP equivalents.h-1.g cells-1 respectively. The carbon substrate-dependent variations in YmaxATP are probably due to differing energy requirements for macromolecular biosynthesis. Oxygen-limited (glycerol-grown) cultures exhibited similar YmaxATP and K values to those of glycerol-limited cultures. YmaxATP values for ammonium- and sulphate-limited cultures were generally similar to those for carbon-limited growth with the same carbon substrate but values for M were substantially higher (viz 14.9-30.8 mmole ATP equivalents.h-1 .g cells-1). It is concluded that neither YmaxATP nor M are constant values for E. coli W. YmaxATP was always considerably lower than the theoretical value, calculated for macromolecular biosynthesis; the magnitude and possible nature of energy-requiring processes which contribute to this difference are discussed.
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