Abstract
In this study, we constructed recombinant luminescent Escherichia coli with T7, T3, and SP6 promoters inserted between tol and lux genes as toluene biosensors and evaluated their sensitivity, selectivity, and specificity for measuring bioavailable toluene in groundwater and river water. The luminescence intensity of each biosensor depended on temperature, incubation time, ionic strength, and concentrations of toluene and coexisting organic compounds. Toluene induced the highest luminescence intensity in recombinant lux-expressing E. coli with the T7 promoter [T7-lux-E. coli, limit of detection (LOD) = 0.05 μM], followed by that in E. coli with the T3 promoter (T3-lux-E. coli, LOD = 0.2 μM) and SP6 promoter (SP6-lux-E. coli, LOD = 0.5 μM). Luminescence may have been synergistically or antagonistically affected by coexisting organic compounds other than toluene; nevertheless, low concentrations of benzoate and toluene analogs had no such effect. In reproducibility experiments, the biosensors had low relative standard deviation (4.3–5.8%). SP6-lux-E. coli demonstrated high adaptability to environmental interference. T7-lux-E. coli biosensor—with low LOD, wide measurement range (0.05–500 μM), and acceptable deviation (− 14.3 to 9.1%)—is an efficient toluene biosensor. This is the first study evaluating recombinant lux E. coli with different promoters for their potential application in toluene measurement in actual water bodies.
Highlights
The large-scale consumption of petroleum-derived fuels has led to groundwater and soil contamination through their leakage from fuel tanks and pipelines
Comparison of time-dependent induction of our three recombinant luminescent E. coli strains with toluene Figure 1 illustrates the construction of the three recombinant plasmids
The results demonstrated that the toluene concentration determined using our biosensors and through gas chromatography (GC)–mass spectrometry (MS) demonstrated excellent correlation (r2 > 0.998); the deviation between the toluene concentrations measured through GC–MS and those measured using T7-lux-E. coli, T3-lux-E. coli, and SP6-lux-E. coli was − 14.3 to 9.1%, − 10.7 to 26.7%, and − 3.6 to 4.2%, respectively
Summary
The large-scale consumption of petroleum-derived fuels has led to groundwater and soil contamination through their leakage from fuel tanks and pipelines. Because of its moderate solubility in water and toxicity, toluene is a petrochemical contaminant of particular concern [1]. Toluene can be carcinogenic, can exhibit mutagenic properties, and can damage the kidney, liver, and central nervous system [2]. In Taiwan, environmental agencies have set acceptable limits for toluene in drinking water and groundwater at considerably low levels (7.6–10.9 μM) [3, 4]. Conventional analytical techniques, such as gas chromatography (GC) and high-performance liquid chromatography, are sensitive and reliable for toluene detection but are time-consuming, expensive, and laboratorybound, and they require large equipment and specialized training [5, 6].
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