Detection of 4-chlorobenzoate using immobilized recombinant Escherichia coli reporter strains

A test for the detection of 4-chlorobenzoic acid (4-CBA) based on reporter microorganisms is developed. A 1.7-kb DNA fragment, upstream of the dehalogenase operon from Arthrobacter sp. strain SU, is fused to the promoterless luciferase operon of Vibrio fischeri. This reporter construct is introduced into two different Escherichia coli strains (UTL2 and RFM443), which specifically respond to the presence of 4-CBA with light emission. The development and optimization of an alginate-based immobilization procedure of the microorganisms in microtiter plates is described. In this format, 4-CBA can be detected in the concentration range of 113 μM-3.6 mM. The membrane leaky mutant UTL2 of E. coli transformed with the reporter construct improves the detection limit to 28 μM when 150 mM KNO₃ is added to the medium.