Fig. 2.

Whole cell biosensing of protocatechuate inP. putida. (A) Response plot of different generations of the PcaU-based sensor in P. putida when exogenously dosed with PCA. UI (for uninduced cultures) refers to microbial cells grown in the absence of exogenously supplemented PCA. (B) Specificity evaluation of the evolved sensor, pPcaU1.2, against similar aromatic molecules. Error bars in (A) and (B) are standard deviations from more than three independent experiments performed by multiple researchers. (C) Schematic showing the ability of 4-hydroxybenzoate to be metabolized to PCA and beyond depending on the genotype of P. putida strains, namely CJ182 (no conversion to PCA, dotted box), native P. putida KT2440 (conversion to PCA, which is then converted to downstream metabolites, dashed box) and CJ072 (accumulates PCA, solid box). (D) Intracellular accumulation of PCA and sensor response in P. putida strains. Error bars are standard deviations from two independent experiments performed by different researchers on different days. UI (for uninduced cultures) refers to microbial cells grown in the absence of exogenously supplemented 4HB. RFU: Relative Fluorescence Units.