A simple chromogenic whole-cell arsenic biosensor based on Bacillus subtilis

Arsenic contaminated ground water is a serious public health issue, and recent estimates place 150 million people worldwide at risk. Current chemical field test kits do not reliably detect arsenic at the lower end of the relevant range, and may generate toxic intermediates and waste. Whole-cell biosensors potentially provide an inexpensive, robust and analyte-specific solution to this problem. The second generation of a Bacillus subtilis -based arsenic biosensor, designated Bacillosensor-II, was constructed using the native chromosomal ars promoter, arsR and the reporter gene xylE encoding catechol-2,3-dioxygenase. Within four hours, Bacillosensor-II can detect arsenic in the form of arsenate (AsO 4 3- ) at levels more than one order of magnitude below the recommended safe limit for drinking water suggested by the World Health Organisation (10 μg/L). Detection is reported by the enzymatic conversion of the inexpensive substrate catechol to 2-hydroxy- cis,cis -muconic semialdehyde, a bright yellow product visible by eye. We hope that this work will aid in developing a simple inexpensive field test kit for screening of drinking water for arsenic contamination.