Biosensors used in this study. IPTG- (A), ATc- (B) and HSL- (C) biosensor constructs and functioning. The BioBrick™ code (BBa_code) of the biosensor-encoding sequences and the microbial host are reported for each construct. All of them were used in the pSB3K3 medium-copy BioBrick™ vector backbone with the p15A replication origin and kanamycin resistance marker. Symbols: curved arrows represent promoters, straight arrows represent coding sequences, ovals represent RBSs, octagons represent transcriptional terminators, “&” means that both inducer and gene product are required to activate the promoter, circles represent chemical inducers, bulbs represent a red fluorescence output and finally dashed lines represent MG1655-Z1 genomic DNA. PLlacO1 and PLtetO1 are synthetic promoters that can be repressed by LacI and TetR, respectively. PluxI is the wild type luxI promoter from Vibrio fischeri that can be activated by the LuxR-HSL complex. In the HSL-biosensor (panel C), luxR expression was always induced by 500 μM of IPTG, as gene expression is driven by the PLlacO1 promoter.