Green Fluorescent Protein as a Noninvasive Stress Probe in Resting Escherichia coli Cells

We constructed and characterized three stress probe plasmids which utilize a green fluorescent protein as a noninvasive reporter in order to elucidate Escherichia coli cellular stress responses in quiescent or resting cells. Cellular stress levels were easily detected by fusing three heat shock stress protein promoter elements, those of the heat shock transcription factor ς(32), the protease subunit ClpB, and the chaperone DnaK, to the reporter gene gfp(uv). When perturbed by a chemical or physical stress (such as a heat shock, nutrient [amino acid] limitation, or addition of IPTG [isopropyl-β-d-thiogalactopyranoside], acetic acid, ethanol, phenol, antifoam, or salt [osmotic shock]), the E. coli cells produced GFPuv, which was easily detected within the cells as emitted green fluorescence. Temporal and amplitudinal mapping of the responses was performed, and the results revealed regions where quantitative delineation of cell stress was afforded.