Timing and dynamics of single cell gene expression in the arabinose utilization system
Judith A. Megerle 1*, Georg Fritz 2, Ulrich Gerland 2, Kirsten Jung 3 and Joachim O. Radler 3
1 Ludwig-Maximilians-Universitat Munchen
2 Universitat zu Koln
3 Ludwig-Maximilans-Universitat Munchen
* To whom correspondence should be addressed. E-mail: judith.megerle{at}physik.uni-muenchen.de.
Submitted on December 5, 2007
Revised on January 12, 2008
Accepted on 23 April 2008
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Abstract |
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The arabinose utilization system of E. coli displays a stochastic "all or nothing" response at intermediate
levels of arabinose, where the population divides into a fraction catabolizing the sugar
at a high rate (ON state) and a fraction not utilizing arabinose (OFF state). Here we study this
decision process in individual cells, focusing on the dynamics of the transition from the OFF to the
ON state. Using quantitative time-lapse microscopy, we determine the time delay between inducer
addition and fluorescence onset of a GFP reporter. Through independent characterization of the
GFP maturation process, we can separate the lag time caused by the reporter from the intrinsic
activation time of the arabinose system. The resulting distribution of intrinsic time delays scales
inversely with the external arabinose concentration, and is compatible with a simple stochastic
model for arabinose uptake. Our findings support the idea that the heterogeneous timing of gene
induction is causally related to a broad distribution of uptake proteins at the time of sugar addition.
Key Words:
GFP maturation, cell-to-cell variation, positive feedback, quantitative model, time-delay, time-lapse microscopy
