Freeze-dried recombinant bacteria for on-site detection of phenolic compounds by color change

We herein report the development of a recombinant bacterial biosensor for the rapid and easy detection of phenolic compounds in the field. A plasmid was designed to encode a beta-galactosidase reporter gene under the control of capR, an activator involved in phenolic compound degradation. The construct was transformed into Escherichia coli, and transformed cells were stored after being freeze-dried in the presence of sucrose. For detection of phenolic compounds, the cells were rehydrated, and used instantly, without any growth step. In the presence of 0.1 microM-10mM phenol, we observed a red color from hydrolysis of chlorophenol red beta-D-galactopyranoside (CPRG) or an indigo color from hydrolysis of X-galactopyranoside (X-gal). Other phenolic compounds could be detected by this system, including catechol, 2-methylphenol, 2-chlorophenol, 3-methylphenol, 2-nitrophenol, and 4-chlorophenol. These results suggest that this novel bacteria biosensor may be useful for easy, on-site detection of phenolic compounds without the need for unwieldy equipment or sample pretreatment. Indeed, biosensor systems involving beta-galactosidase-expressing freeze-dried recombinant bacteria could prove useful for the in situ detection of many more compounds in the future.