The Energetics of Escherichia coli during Aerobic Growth in Continuous Culture

Abstract

1 The energetics of Escherichia coli W growing aerobically in continuous culture have been investigated. Conditions were chosen such that growth was limited by the availability of carbon or oxygen (energy-limited cultures), or of ammonium or sulphate ions (excess energy cultures). 2 Under glycerol-limited conditions Y^max_O2(true molar growth yield with respect to oxygen) and Y^max_ATP (true molar growth yield with respect to ATP equivalents) were 50.9 g cells · mol O₂⁻¹ and 12.7 g cells mol ATP equivalents⁻¹ respectively; these values were not substantially altered during growth limited by oxygen. ammonium or sulphate. In contrast, M (the energy requirement. for maintenance purposes) increased from approximately 2 mmol ATP equivalents · h⁻¹ g.cell⁻¹ during energy-limited growth to 16.8 and 30.8 mmole ATP equivalents h⁻¹ g cells⁻¹ when growth was limited by ammonium and sulphate ions respectively. 3 Replacement of glycerol by other limiting carbon sources caused Y^max_ATP to alter within the range 13.9 (glucose) to 7.1 (acetate) g cells mol ATP equivalents⁻¹ in the order glucose > galactose > arabinose > fructose > glycerol > fumarate > lactate > pyruvate > acetate. In each case the experimental value of Y^max_ATP was ≤ 55% of the theoretical value calculated from the known energy requirements for the biosynthesis of cell materials. 4 It is concluded from these results that neither M nor Y^max_ATP are constant values for E. coli. M varies with the energy supply, being highest under excess energy growth conditions where it may reflect energy wastage by the cell. On the other hand, Y^max_ATP varies with the nature of the growth substrate and thus reflects the different energy requirements for the synthesis of cell material from different carbon sources