Enhancement of the multi-channel continuous monitoring system through the use of Xenorhabdus luminescens lux fusions

The enhancement of the multi-channel continuous toxicity monitoring system developed previously was studied. To achieve better and more stable results from the system, the use of thermo-lux fusion strains that express the luxCDABE genes from Xenorhabdus luminescens was evaluated. A total of six recombinant Escherichia coli strains with the promoters from three oxidative-stress responsive genes, i.e. the katG, sodA and pqi-5 genes, fused to either the lux genes from Vibrio fischeri or X. luminescens were characterized and their responses to different chemicals compared. It was found that the basal level bioluminescence (BL) from the thermo-lux fusion strains was always higher while that of the V. fischeri lux strains were always near or below the lower limit of detection of the system. For example, the katG::V. fischeri lux strain, DPD2511, gave no discernible response due to its low level expression while a fusion of the katG promoter with the X. luminescens lux operon was clearly responsive and capable of detecting hydrogen peroxide down to about 1 ppm. The use of the thermo-lux strains found them to be as sensitive as the V. fischeri lux strains while providing a brighter, more stable basal level bioluminescence, making the analysis and monitoring of water-borne toxicity more reliable.