Improved bacterial bioreporters for the remote detection of buried explosive devices

Landmines and explosive remnants of war pose a global problem which claims many casualties long after the conflict has ended. Current approaches for the location of landmines, such as metal detection, require physical presence at the minefield and therefore involve high risk to personnel; these methods are also costly, time consuming, and have a high rate of false positive results. The development of alternative technologies for efficient remote detection of buried explosive devices is thus urgently needed.

Most landmines contain 2,4,6-trinitrotoluene (TNT) as the main explosive component, as well as its production by product 2,4-dinitrotoluene (DNT). Over time, the more volatile DNT leaks out of the landmine casing and accumulates in the soil above it, serving as an excellent "signature molecule" for its presence.

Over the last few years we have developed Escherichia coli-based microbial bioreporters for landmine detection. These sensor strains harbour fusions of gene promoters (yqjF and azoR), induced by the presence of DNT metabolites, to the microbial bioluminescence luxCDABEG reporter gene cassette. Using a combinations of molecular biology techniques such as DNA random mutagenesis, DNA shuffling and introduction of quorum sensing elements we were able to reduce the DNT detection threshold by over 100-fold. In addition, the use of luxCDABEG reporter genes from different luminescent bacteria resulted in a significant expansion of the temperature operation range. Encapsulation of the bacteria in alginate-based beads represent a promising technology for future detection of buried landmines.