Landmines left over from past conflicts or still being fought pose a silent threat to millions of people around the world. With the help of bacteria that glow in their presence, these hidden dangers may one day be found and safely removed or destroyed become.
Researchers at the Hebrew University of Jerusalem have spent a decade developing live land mine sensors using E. coli bacteria. In current studies, they describe their recent advances. Using genetic engineering, they can turn any bacterium into “a miniature firefly,” in the presence of a chemical associated with the explosive, said Shimshon Belkin, the research chief microbiologist at the Hebrew University.
In 2019, more than 5,500 people were killed or injured by land mines and explosive remnants of the war, and 80 percent of them were civilians, according to the International Campaign to Ban Landmines. Anti-personnel mines that are only a few centimeters wide and easy to hide are particularly dangerous. Estimates of the number of landmines buried worldwide vary, but they range as high as 110 million.
Many strategies have been tried to locate landmines, such as using metal detectors and training sniffer dogs, including an award-winning rat that helped find 71 landmines before she retired. Each method balances benefits with risks and costs.
The idea of rewiring bacteria to detect landmines came from Robert Burlage, then at Oak Ridge National Laboratory in Tennessee. In the mid-1990s, Dr. Make sure you make bacteria glow in response to organic waste and mercury. While looking for a new application for this technique, he came up with the idea of targeting landmine chemicals.
Although Dr. Burlage carried out a few small field tests, he was unable to raise any further funds and moved on. “My story of suffering,” said Dr. Burlage, now a professor at Concordia University Wisconsin.
The work of Dr. Burlage was an inspiration to the Israeli researchers, and he says he wishes them all the best in their efforts to advance the technology.
Bacteria are cheap and dispensable and can be spread over a lot of soil. And they respond relatively quickly – within hours or up to a day they either light up or not.
In studies published in Current Research in Biotechnology and Microbial Biotechnology last year, Dr. Belkin and his team tinkered with two key components of the E. coli genetic code: pieces of DNA called “promoters” that act as on / off switches for genes and “reporters” that trigger light-emitting responses. To achieve this effect, the researchers borrowed genes from marine bacteria that naturally emit light into the ocean.
Scientists tuned the bacteria to a chemical called 2,4-dinitrotoluene, or DNT, a volatile by-product of trinitrotoluene, or TNT. Over time, DNT vapor seeps into the ground surrounding a land mine and the bacteria can sniff it out.
Instead of wandering around freely, the bacteria are immobilized in tiny gelatinous globules that they feed while they work. Each bead, about one to three millimeters in diameter, contains about 150,000 active cells.
These latest harvests of genetically modified bacteria are faster and more sensitive than bacteria in the group’s previous field tests, said Dr. Belkin. And the scientists no longer need a laser signal to activate the glow.
One of the key challenges the group is working on is how to safely locate the bioluminescent bacteria in a real minefield. When they spot landmines, their glow is so dim that the light from the moon, stars, or nearby cities could drown it out.
To address this problem, Aharon J. Agranat, a bio-engineer at the Hebrew University, and other researchers reported in the journal Biosensors and Bioelectronics in April that they had developed a device that shields the bacteria and detects their glow. This sensor system can then report its results to a nearby computer, but it has not been tested outside of a laboratory setting.
The researchers also recently conducted field tests in Israel, working with the Israeli army to ensure the safety of the experiments, as well as with an Israeli defense company. The results of these tests were not published, but Dr. Belkin called them “generally very successful”.
In the future, the team hopes to be able to use bacteria sensors in a minefield with drones so that people don’t have to come near them.
Dr. Decades ago, Burlage came across another subject that the group at the Hebrew University is still working on today: temperature. Israeli bacteria sensors only work at around 59 to 99 degrees Fahrenheit, which means researchers need to figure out how to adapt their systems to scorching desert conditions.
Israeli bioengineers also acknowledge that their bacteria sensors could be used for both humanitarian and military purposes. DARPA, the Defense Advanced Research Projects Agency, sponsored their research.
Nonetheless, landmine bacterial sensors show how the field of synthetic biology “has grown by leaps and bounds over the past few decades,” said Dr. Timothy K. Lu, Co-Founder of Senti Biosciences and Bioengineer at the Massachusetts Institute of. Technology, which was not involved in these studies.
“It’s super exciting and I hope that these types of applications will move from the lab to the real world,” said Dr. Lu.