Growth and eilA reporter assay

Growth media used in this study were DMEM (Invitrogen, UK), LB, and a 1:1 mix of LB with DMEM. The eilA reporter construct contains a ~500 bp fragment upstream of the eilA promoter from the CE10 strain of E. coli (Accession number NC017646) that was cloned into a plasmid (pAJR70) used in a previous study for the assessment of transcription of ETT1 operons by enhanced green fluorescent protein (GFP) monitoring from liquid culture⁴². The different bacterial strains were transformed with this plasmid using standard methods. Chloramphenicol (25 µg/ml) was added to media when required for the selection of strains containing the eilA reporter. Induction of GFP in the different media at 37 °C was measured using a fluorescence plate-reader (FLUOstar Optima; BMG; Labtech, UK). Optical densities and fluorescence were recorded every 24 minutes for 9 hours. Measurements from bacteria transformed with the promoterless pAJR70 showed there was no signal produced above that of the fluorescence of bacteria alone which was subtracted from all readings.