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J. Bacteriol. doi:10.1128/JB.00746-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Cell-to-cell Heterogeneity in Growth Rate and Gene Expression in Methylobacterium extorquens AM1

Department of Bioengineering, Department of Microbiology, and Department of Chemical Engineering, Microscale Life Sciences Center, University of Washington, Seattle, WA 98195-2180

^* To whom correspondence should be addressed. Email: lidstrom{at}u.washington.edu.

	Abstract

Cell-to-cell heterogeneity in gene expression and growth parameters was assessed in the facultative methylotroph, Methylobacterium extorquens AM1. A transcriptional fusion between a well-characterized methylotrophy promoter (P_mxaF) and gfp_uv was used to assess single cell gene expression. Using a flow-through culture system and laser scanning microscopy, data on fluorescence and cell size were obtained over time through several growth cycles on cells grown on succinate or methanol. Cells were grown continuously with no discernable lag between divisions with high cell-to-cell variability observed for cell size at division (2.5 fold range), division time, and growth rates. When individual cells were followed over multiple division cycles, no direct correlation was observed between growth rate before a division and subsequent growth rate, or between cell size at division and subsequent growth rate. The cell-to-cell variability for GFPuv fluorescence from the P_mxaF promoter was less, with a range on the order of 1.5-fold. Fluorescence and growth rate was also followed during a carbon shift experiment, in which cells growing on succinate were shifted to methanol. Variability of response was observed and growth rate at the time of the shift from succinate to methanol was a predictor of response. Higher growth rates at the time of substrate shift resulted in greater decreases in growth rates immediately after the shift, but full induction of P_mxaF-gfp_uv was achieved faster. These results demonstrate that in M. extorquens, physiological heterogeneity at the single-cell level plays an important role in determining population response to this metabolic shift.

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