Landmines left by past conflicts – or those still ongoing – pose silent threats to millions of people around the world. With the help of bacteria that glow in their presence, these hidden dangers can one day be found and safely removed or destroyed.
Researchers at the Hebrew University of Jerusalem have spent a decade developing living landmine sensors using E. coli bacteria. In recent studies, they describe their latest progress. Using genetic engineering, they can turn each bacteria into “a miniature firefly” in the presence of a chemical associated with explosives, said Shimshon Belkin, the Hebrew University microbiologist who is leading the research.
In 2019, more than 5,500 people were killed or injured by landmines and explosive remnants of war, and 80% of them were civilians, according to the International Campaign to Ban Landmines. Particularly dangerous are anti-personnel landmines, which are only a few centimeters in diameter and can be easily concealed. Estimates vary for the global number of buried landmines, but they stand at 110 million.
Many strategies have been tried to locate landmines, such as using metal detectors and training detection animals, including an award-winning rat who helped locate 71 landmines before his retirement. Each method balances the benefits with the risks and costs.
The idea of rewiring bacteria to detect landmines originated with Robert Burlage, then at Oak Ridge National Laboratory in Tennessee. In the mid-1990s, Dr. Burlage worked on igniting bacteria in response to organic waste and mercury. In search of a new application for this technique, he came up with the idea of trying to target chemicals from landmines.
Although Dr Burlage did a few small field tests, he couldn’t get more funding and moved on. “My story of doom,” said Dr. Burlage, now a professor at Concordia University in Wisconsin.
Dr Burlage’s work has been an inspiration to Israeli researchers, and he says he wishes them well in their efforts to advance the technology.
Bacteria are cheap and consumable and can spread over a lot of ground. And they’re relatively quick to report – within hours or up to a day, they may or may not glow.
In studies published last year in Current Research in Biotechnology and Microbial Biotechnology, Dr. Belkin and his team describe the tinkering with two key components of the genetic code of E. coli: pieces of DNA called “promoters” that act as on / off switches. for genes and “reporters” that trigger light-emitting reactions. To produce this effect, the researchers borrowed genes from marine bacteria that naturally emit light into the ocean.
Scientists adapted the bacteria to a chemical called 2,4-dinitrotoluene, or DNT, a volatile byproduct of trinitrotoluene, or TNT. Over time, the DNT vapor seeps into the soil surrounding a landmine and bacteria can sniff it out.
Rather than roaming freely, the bacteria are immobilized in tiny gelatin-like beads that nourish them as they work. Each bead, about one to three millimeters in diameter, contains about 150,000 active cells.
These latest cultures of genetically modified bacteria react faster and are more sensitive than bacteria in the group’s first field tests, Dr Belkin said. And scientists no longer need to use a laser signal to activate the glow.
One of the main challenges the group is working to overcome is to safely locate bioluminescent bacteria in a real minefield. When they detect landmines, their glow is so faint that light from the moon, stars, or nearby cities could drown it out.
To help solve this problem, Aharon J. Agranat, a bioengineer at Hebrew University, and other researchers reported in April in the journal Biosensors and Bioelectronics that they had developed a device that protects bacteria and detects their bacteria. glow. This sensor system can then report its findings to a nearby computer, but it has not been tested outside of a lab.
Researchers also recently conducted field tests in Israel, working with the IDF to provide security for the experiments, as well as an Israeli defense company. The results of these tests have not been published, but Dr Belkin called them “generally very successful”.
In the future, the team hopes to use drones to deploy bacteria sensors in a minefield, eliminating the need for humans to come close.
Dr Burlage came across another problem decades ago that the Hebrew University group still grapples with today: temperature. Israeli bacteria sensors only work around 59 to 99 degrees Fahrenheit, which means researchers will have to figure out how to adapt their systems to more scorching desert conditions.
Israeli bioengineers also recognize that their bacteria sensors could be used for humanitarian and military purposes. DARPA, the Defense Advanced Research Projects Agency, has helped fund their research.
Nonetheless, bacteria sensors for landmines illustrate how the field of synthetic biology has advanced “by leaps and bounds over the past few decades,” said Dr Timothy K. Lu, co-founder of Senti Biosciences and engineer in biology at the Massachusetts Institute of Technology, who did not participate in these studies.
“It’s super exciting, and I hope to see these kinds of applications start to migrate from the lab to the real world,” said Dr Lu.