Fig. 6.

TCS tuning expands the detection range of an engineered soil fertilizer biosensor. a Experimental protocol for the incubation of bacteria with fertilized soil, subsequent purification via filtration, selection by mCherry fluorescence, and measurement of sfGFP levels (Methods). b Soil was fertilized with different amounts of nitrate as specified by the manufacturer. The level of fertilization was then measured with a B. subtilis strain expressing the NarXL-YdfI TCS with wild-type (black) and C415R (blue) NarX variants (Fig. 2a; Supplementary Fig. 12). This was compared to a previously measured standard curve of nitrate response to calculate a bacterially reported nitrate concentration from the fertilizer (Supplementary Note 2; Supplementary Fig. 12). The relationship between the actual and bacterially reported values is shown. Points represent the mean and error bars the SEM of experiments on three separate days