Detection of 2,4-dichlorophenoxyacetic acid herbicide using a FGE-sulfatase based whole-cell Agrobacterium biosensor.

2,4-Dichlorophenoxyacetic acid (2,4-D)has been widely used as herbicide for agricultural purposes. Currently, the available methods for detecting 2,4-D require multi-step sample preparations and expensive instruments. Using a whole cell biosensor is an interesting approach that is straightforward and simple to use. In this study, we constructed a genetic-based Agrobacterium tumefaciens biosensor based on a cadA promoter and cadR regulator from Bradyrhizobiumsp. strain HW13 (2,4-D degrader) with the formylglycine generating enzyme (FGE)-sulfatase as the reporter genes. The performance of the biosensor was further improved through direct evolution of the cadR activator. The detection limit of cadR mutants for phenoxyacetic acid herbicides including 2,4-D and 4-Chlorophenoxyacetic acid (4-CPAA) were 1.56 μM (an eight-fold improvement compared to using wild-type CadR).The biosensor could detect 2,4-D in environmental samples without encountering interference from other complex compounds. TheAgrobacteriumbiosensor was also stable after storing in a simple Luria-Bertani (LB) medium at 4 °C for 30 days in which the activity remained at 82% when exposed to 100 μM of 2,4-D.This novel biosensor,with its high stability under simple storage conditions,exhibits promising potential for use as an inexpensive and easy-to-use tool to screen for 2,4-D contamination in environmental sources.