Introduction of quorum sensing elements into bacterial bioreporter circuits enhances explosives’ detection capabilities

A possible solution for the standoff detection of buried landmines is based on the use of microbial bioreporters, genetically engineered to emit a remotely detectable optical signal in response to trace amounts of explosives’ signature chemicals, mostly 2,4-dinitrotoluene (DNT). Previously developed DNT sensor strains were based on the fusion of a DNT-inducible gene promoter to a reporting element, either a fluorescent protein gene or a bacterial bioluminescence gene cassette. In the present study, a different approach was used: the DNT-inducible promoter activates, in Escherichia coli, the quorum-sensing luxI and luxR genes of Aliivibrio fischeri. N-Acyl homoserine lactone (AHL), synthesized by LuxI, combines with LuxR and activates the bioluminescence reporter genes. The resulting bioreporter displayed a dose-dependent luminescent signal in the presence of DNT. Performance of the sensor strain was further enhanced by manipulation of the sensing element (combining the E. coli DNT-inducible azoR and yqjF gene promoters), by replacing the luminescence gene cassette of Photorhabdus luminescens luxCDABE with A. fischeri luxCDABEG, and by introducing two mutations, eutE and ygdD, into the host strain. DNT detection sensitivity of the final bioreporter was over 340-fold higher than the original construct.