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| Construction of an Escherichia coli Biosensor for Cd2+ and Sensitivity Analysis by Low-temperature Induction |
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Abstract Microbial whole-cell sensor has been widely used to assess bioavailability and risk of toxic elements, but their environmental use is still limited due to the low sensitivity and poor selectivity. Here, Escherichia coli BL21 (DE3) was employed as a bacteria strain of the sensor, the expression vector pETDuet-1 as an initial skeleton, the DNA fragment O/P-cadC consisting of the promoter/operator of the cad operon and cadC gene as a sensing module, and gfp as a reporter gene to construct a new type of microbial whole-cell sensor in response to Cd2+. The GFP fluorescence of the sensor cells induced by Cd2+ was measured by fluorescence emission spectroscopy and fluorescence microscopy, and the sensitivity changes of the biosensor induced by Cd2+ at low temperature was analyzed. Results showed that a GFP-based microbial whole-cell sensor E. coli BL21(DE3)_pO/P-cadC::gfp was successfully developed, which exhibited strong green fluorescence exposed to Cd2+ and dose-dependent effects of green fluorescence on the concentration of Cd2+. The lowest detectable concentration of the biosensor at 37 ℃ was 1 mmol/L, whereas the lowest detectable concentration decreases to 1 μmol/L at 25 ℃, and 10 nmol/L at 15 ℃. The sensitivity of the biosensor induced with lower temperature is improved obviously. This study indicated that the constructed E. coli whole-cell sensor could dose-dependently and selectively respond to Cd2+. The temperature has an important effect on the fluorescence intensity of the sensor cells, and the sensitivity of the sensor can be improved significantly at low temperature. This provides reference for the detection of bio-availability of Cd2+ in the environment by using the microbial whole-cell sensor.
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Received: 17 August 2018
Published: 20 November 2018
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