Fig. 1

Molecular mechanism conferring resistance to β-lactams and genetic design of the biosensor constructs. a: The BlaR1/BlaI regulatory system in its inactive state: when no β-lactam is present, the BlaI repressor binds to the intergenic promoter regions and inhibits gene expression in both directions. The β-lactamase BlaZ is not synthesized. b: The BlaR1/BlaI regulatory system in its active state: the β-lactam (here meropenem in grey) binds to the periplasmic BlaR1 sensor domain (structure predicted using SWISS-MODEL). This results in the activation of the cytoplasmic BlaR1 protease domain by autocleavage and subsequent degradation of BlaI. This results in expression and hence production of BlaR1, BlaI and the β-lactamase BlaZ. BlaZ is secreted and inactivates the β-lactam. c: (1) Initial biosensor design present in the two strains TMB3641 (Biosensor 1) and TMB3713 (Biosensor 1 ΔpenP). The blaZ gene was replaced by the lux operon serving as readout. (2) Improved biosensor design of strains TMB5608 (Biosensor 2), TMB5610 and TMB5611 (Biosensor 2 ΔpenP). Strain TMB5610 is an inducible biosensor version, enabling expression of blaR1 in presence of xylose. The two genes blaR1 and blaI were codon optimized, genetically separated and placed under the control of constitutive promoters. Again, P_blaZ-lux serves as readout