SUMMARY: Fluctuations in cell volume during exponential growth of K12 changed the effectiveness of the continuous-flow centrifugation method for preparing synchronous cultures. Rates of oxygen uptake in synchronous cultures were measured using an electrode system open to the atmosphere. In synchronous cultures of both the parental strain and an adenosine triphosphatase-deficient mutant, which was incapable of oxidative phosphorylation, respiration rates doubled during the cell cycle but oscillated with a periodicity of approximately half a cycle. Synchronous cultures of the parental strain growing on glycerol and Casamino acids showed a stepwise pattern of oxygen consumption. Continuous flow centrifugation did not markedly affect the increases in the numbers and respiration rates of cells in synchronous cultures. Respiratory oscillations also occurred on inoculation of a late-stationary phase culture into fresh medium, although synchronous division was not observed. The possible mechanisms underlying respiratory fluctuations under different growth conditions are discussed.


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