In Sri Lanka, fluoride is found to be a major groundwater contaminant that causes significant health problems and, thus safe consumption of drinking water must be ensured. Therefore, adopting an inexpensive and rapid solution to monitor the presence of fluoride in drinking water is vital to reduce the vulnerability of communities to fluoride dependent diseases. However, most of the widely employed fluoride detection methods suffer from interference with other anions, which greatly limits the scope of their use. We have developed a fluoride riboswitch-based whole-cell biosensor as a new approach for monitoring fluoride, with high accuracy, selectivity, and sensitivity. The method of detection utilizes an E. coli mutant carrying a plasmid cloned with fluoride responsive riboswitch, coupled to the lacZ reporter gene. Fluoride binding to the aptamer domain induces riboswitch-mediated downstream expression of lacZ. The enzymatic activity was measured by the turn-over of Ortho-nitrophenyl-β-D-galactopyranoside (ONPG), resulting in the yellow color product Ortho-nitrophenol (ONP). The absorbance of ONP was measured at 420 nm and was used to quantify the fluoride content. The calibration curve showed a significant correlation between the absorbance of ONP and fluoride levels in the standards (R2= 0.9905) for the fluoride concentrations ranging from 5–100 μM. Next, the fluoride content of water samples obtained from various regions was measured using the biosensor. The highest level of groundwater fluoride was found in the Anuradhapura district (5.7 ppm), in the north-central province of Sri Lanka. The experimentally determined fluoride levels are in agreement with the ion-selective electrode readings and the reported values. Unlike other fluoride detection methods, this novel riboswitch-based biosensor is selectively activated by fluoride but rejects other small anions, including chloride and hydroxide ions. This work provides a critical proof-of-principle for employing the fluoride selective riboswitch-based whole-cell biosensor to accurately monitor environmental fluoride.

Riboswitch-based whole-cell biosensor for detection of fluoride in drinking water

ACS Spring Meeting 2021

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