Kinetic, dynamic, and pathway studies of glycerol metabolism by Klebsiella pneumoniae in anaerobic continuous culture: I. The phenomena and characterization of oscillation and hysteresis.
Oscillation and hysteresis phenomena are observed in the anaerobic continuous fermentation of glycerol by Klebsiella pneumoniae in long-term cultivations under a variety of conditions. In this work, the conditions for the occurrence of these phenomena are reported and the patterns of cell growth and metabolism under oscillation are characterized. During an oscillation period, the formation rates of CO(2), H(2), and formate and the consumption rate of alkali periodically pass values of maxima and minima, the latter being close to zero. The formation of biomass and fermentation products such as 1,3-propanediol, acetate, and ethanol also undergo periodic changes which shift maxima and minima. Sustained oscillation occurs only under conditions of substrate excess within a distinct regime. At pH 7.0, it is only found at dilution rates above 0.15 h(-1) under the experimental conditions. At lower pH values, oscillations are more likely to happen, even at a relatively low dilution rate and low substrate excess. Whereas the amplitude of oscillations at pH 7.0 depends on both the dilution rate and the residual glycerol concentration (C(Glyc)) the interval of oscillations appears to be only a function of C(Glyc). An increase of C(Glyc) in culture damps the oscillation and leads to its disappearance at C(Glyc) = 1100 to 1200 mmol/L (pH 7.0). The operation mode was also found to be an important parameter in determining the stability and actual state of the culture, resulting in hysteresis under certain conditions, particularly at low pH values. Generally, a large perturbation of cultivation conditions tends to cause oscillation and hysteresis. The results unambiguously demonstrate that the oscillation and hysteresis phenomena shown in this work are bound to genuine metabolic fluctuations of the microorganism. They reveal several differences and new features compared with those reported in the literature and cannot be readily explained by the mechanisms known so far.
Menzel
K
K
Biochemical Engineering Division, Gesellschaft für Biotechnologische Forschung mbH, Mascheroder Weg 1, 38124 Braunschweig, Germany.
Zeng
A P
AP
Biebl
H
H
Deckwer
W D
WD