Comparison of the transient responses of Escherichia coli to a glucose pulse of various intensities.

Dynamic stimulus-responses of Escherichia coli DPD2085, yciG::LuxCDABE reporter strain, to glucose pulses of different intensities (0.08, 0.4 and 1 g L(-1)) were compared using glucose-limited chemostat cultures at dilution rate close to 0.15 h(-1). After at least five residence times, the steady-state cultures were disturbed by a pulse of glucose, engendering conditions of glucose excess with concomitant oxygen limitation. In all conditions, glucose consumption, acetate and formate accumulations followed a linear relationship with time. The resulting specific uptake and production rates as well as respiratory rates were rapidly increased within the first seconds, which revealed a high ability of E. coli strain to modulate its metabolism to a new environment. For transition from glucose-excess to glucose-limited conditions, the cells rapidly re-established its pseudo-steady state. The dynamics of transient responses at the macroscopic viewpoint were shown to be independent on the glucose pulse intensity in the tested range. On the contrary, the E. coli biosensor yciG::luxCDABE revealed a transcriptional induction of yciG gene promoter depending on the quantities of the glucose added, through in situ and online monitoring of the bioluminescence emitted by the cells. Despite many studies describing the dynamics of the transient response of E. coli to glucose perturbations, it is the first time that a direct comparison is reported, using the same experimental design (strain, medium and experimental set up), to study the impact of the glucose pulse intensity on the dynamics of microbial behaviour regarding growth, respiration and metabolite productions.