Fig. 2.

Phosphatase-reducing mutations decrease detection threshold in a B. subtilis nitrate sensor. a An engineered B. subtilis nitrate-sensing TCS. The E. coli SK NarX signals to a chimeric RR composed of the N-terminal Receiver (REC) domain of E. coli NarL fused to the C-terminal DNA binding domain (DBD) of B. subtilis YdfI (Supplementary Fig. 2). Phosphorylated NarL-YdfI activates transcription from the B. subtilis P_ydfJ115 output promoter. b Transfer functions of variants from (a) containing wild-type NarX, NarX(C415R), and NarX(D558V). Points represent the mean and error bars the standard error of the mean (SEM) of experiments on three separate days