Casavant, N. C., G. A. Beattie, G. J. Phillips, and L. J. Halverson. A novel genetic system to ascertain bacterial exposure to environmental pollutants: A life history biosensor. Agronomy Society of America / Crop Science Society of America / Soil Science Society of America Joint Annual Meeting, November 5-9, 2000. Minneapolis, MN. p. 266

We developed a novel bacterial biosensor designed to report on the life history of the biosensor. Exposure to a signal initiates a cascade of events leading to irreversible expression of green florescent protein in the biosensor cell and its progeny. In this system, the Lambda promoter PL
controls gfp expression and is strongly repressed by the Lambda cI repressor. Irreversible gfp expression occurs when an effector signal induces the synthesis of an excisionase/integrase that excises the cI repressor gene. We tested this system using the PBAD promoter of the
arabinose operon and PtbuA1 promoter of the toluene/benzene utilization operon as signal sensitive promoters to direct expression of excisionase/integrase. In the absence of exogenous addition of the signal only 0-2% of the biosensor population spontaneously removes the cI repressor resulting in a false report of signal exposure. Within 24 hours after signal exposure, 99% of the biosensor population has initiated the genetic reprogramming leading to gfp expression; at high arabinose concentrations 90% of the population initiated the genetic reprogramming within four hours. With a rhizosphere competent Enterobacter cloacae strain we have demonstrated that the biosensor is operable during soil colonization and conclude that this system will provide a useful tool in ecological studies.