Figure 3

Time-lapse images. We monitored levels of cfp, yfp, and rfp expression from the construct shown in Figure 1 during growth in a microcolony of E. coli MG1655. This strain has low levels of LacI and no TetR, leaving cfp constitutively active. We grew the microcolonies on agarose pads, using arabinose as a carbon source to ensure AraC induction. (A) The pseudo-colors indicate the expression levels of rfp (red), yfp (green), and cfp (blue). (B) Two-color images, made by adding pairs of images colored as in A, show how each pair of colors varies over time in single cells. Cells appearing yellow, the combination of red and green, reveal the correlation between yfp and rfp due to LacI co-regulation. (C) Correlation between pairs of colors as a function of time calculated across all cells in the microcolony, the error bars represent 90% confidence intervals (Methods). These average correlations persist over several hours of microcolony growth.