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New in landmine detection: E. coli that lights up in presence of explosives

Synthetic biology seeks to reduce human cost of legacy underground arsenal

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Mention E. coli and most people react with dread. In humans, the bacteria can wreak havoc on digestive systems — although healthy people have some of the bacteria in our lower digestive tracts, when the gut becomes overloaded with it, we really feel the effects.

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Ontarians still remember the contaminated water supply issue in Walkerton two decades ago that made more than 2,000 people very ill and killed seven. Heavy rainfall that spring was said to have resulted in agricultural runoff containing E. coli entering the town’s water system. It was the worst public health disaster involving municipal water in Canadian history; blame was attributed to lax management and testing practices that lowered purifying chlorine levels.

A drinking water taps is shut off at Walkerton city hall during the 2000 E. coli outbreak caused by contaminated municipal water.
A drinking water taps is shut off at Walkerton city hall during the 2000 E. coli outbreak caused by contaminated municipal water.

That event does raise the question of whether E. coli can be safely used outside its natural environment.

In Israel, researchers have been trying to put E. coli to good use. Over a decade, they’ve been developing living land mine sensors using the bacteria, the New York Times reports.

With genetic engineering, they “turn each bacterium into ‘a miniature firefly’ in the presence of a chemical associated with the explosives,” the Times quoted Shimshon Belkin, the Hebrew University of Jerusalem microbiologist leading the research.

As many as 80 per cent of people killed by land mines and explosives left after wars were civilians. In 2019, the International Campaign to Ban Landmines says, more than 5,500 people were killed or injured this way, and the underground arsenal still lies unnoticed in many areas of the world — estimates of the numbers still undetected reach as high as 110 million.

Prince Harry remotely detonates a landmine in Angola, during a visit to see the work of landmine clearance charity the Halo Trust, in 2019.
Prince Harry remotely detonates a landmine in Angola, during a visit to see the work of landmine clearance charity the Halo Trust, in 2019. Photo by Dominic Lipinski - Pool /Getty Images

Anti-personnel land mines, which are small and easily buried, are especially dangerous. Metal detectors are most often used to find them, but animals have been trained in detection as well. Magawa, an award-winning rat, helped locate 71 land mines before scurrying off to retirement.

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In his research, Belkin borrowed genes from ocean bacteria that naturally emit light, and remade bits of E. coli’s genetic code to produce the light-emitting reactions.

His team then “attuned the bacteria to a chemical called 2,4-dinitrotoluene, or DNT, a volatile byproduct of trinitrotoluene, or TNT,” the Times writes. “Over time, DNT vapour seeps into soil surrounding a land mine, and the bacteria can sniff it out.”

But the bacteria aren’t just sprayed on acres of ground and left to run off or be blown farther afield. They’re encased in gelatin-like beads, each less than three millimetres across, each containing some 150,000 active cells. And they’re fast to react — within hours, or up to a day; they either glow or they don’t.

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But there are still two major shortcomings.

One is the intensity of the glow, as it is so faint that light from the moon or stars, let alone artificial light from a nearby city, can make it difficult to see.

To overcome this, researchers from the university then developed a protective device for the bacteria that also reports the presence of a glow to a nearby computer (though it hasn’t been tested outside a laboratory setting).

The researchers recently collaborated with the Israeli army to ensure the safety of field experiments — as well as an Israeli defence company. The results of these tests have not been published, but Belkin told the Times they were “generally very successful.”

In future, the team hopes to use drones to deploy these bacteria sensors in a minefield, eliminating the need for humans to get close.

The second problem is temperature. The Israeli bacteria sensors work only from about 15 to 37 degrees Celsius, meaning researchers will need to figure out how to adapt their systems to more scorching desert conditions.

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