We propose an experimental and theoretical study of the
chemotactic network in individual cells of the bacterium Escherichia coli.
We believe that this well-characterized network is an ideal system to explore
a general understanding of more complicated biochemical networks. We would
like to address the issue of the sensitivity of this network to variations
in its biochemical parameters. More specifically, if genetically identical
cells are grown in an identical environment, how similar will their biochemical
characteristics be? Spudich and Koshland (Ref 4) demonstrated individuality
of bacterial cells grown in homogeneous conditions by showing characteristic
behavioral differences which persist over their bacterial lifespan. To
elucidate the origin of this non-genetic individuality, we are planing
quantitative measurements (Fluorescence Correlation Spectroscopy) on single
cells (rather than over a population) to correlate the behavior of a single
cell with the concentration of its network components. We hypothesize that
these behavioral differences have their molecular origin in fluctuations
of the genetic expression of certain network components; these fluctuations
might come from stochasticity of the chemical reactions involved in gene
regulation. Numerical simulations will describe the randomness in the gene
regulation. Using a previous model from our laboratory (Ref 6) that explains
many aspects of bacterial chemotaxis, we will theoretically analyze it
to understand the influence of such randomness on cellular behavior. We
will emphasize a tight comparison of numerical results with quantitative
data from individual cells. |
