Land mines left over from conflicts – or those still being fought – pose silent threats to millions of people around the world. With the help of bacteria that glow in their presence, these potential hazards can one day be found and safely eliminated or destroyed.
Researchers at the Hebrew University of Jerusalem have spent a decade developing live landmine sensors using E. coli bacteria. In recent studies, they describe their latest advancement. Using genetic engineering, they were able to turn each bacterium into “a miniature firefly” in the presence of an explosive-related chemical, said Shimshon Belkin, a University of Microbiologist Hebrew scholar, who led the study, said.
In 2019, more than 5,500 people were killed or injured by landmines and explosive remnants of war, and 80 percent of them were civilians, according to the International Campaign to Ban Mines. Anti-personnel mines, which are only a few inches wide and easily concealed, are particularly dangerous. Estimates vary on the number of land mines buried worldwide, but they are as high as 110 million.
Many strategies have been tested for locating land mines, such as using metal detectors and training detection animals, including an award-winning rat that helped locate 71 land mine before it retires. Each method balances benefits with risks and costs.
The idea of rewinding bacteria to sense soil deposits originated with Robert Burlage, then at Oak Ridge National Laboratory in Tennessee. In the mid-1990s, Dr. Burlage was working on making bacteria glow in response to organic waste and mercury. Looking for a new application for the technique, he got the idea to try targeting soil-mine chemicals.
Although Dr. Burlage conducted a few small field trials, he was unable to secure additional funding and move on. “My miserable story,” said Dr. Burlage, now a professor at Concordia University, Wisconsin.
Dr. Burlage’s work is an inspiration to Israeli researchers, and he says he wishes them success in their efforts to develop the technology.
Bacteria are cheap and consumable and can spread over many surfaces. And they’re relatively quick to report back – within a few hours or up to a day, they glow or they don’t.
In studies published last year in the journal Current Research in Biotechnology and Microiotics Biotechnology, Dr. Belkin and his team describe tinkering with two key components of the E. coli genetic code: fragments of DNA. called a “promoter” that acts as an on/off switch for genes, and a “reporter” that drives the glowing responses. To create this effect, the researchers borrowed genes from marine bacteria that emit natural light in the ocean.
The scientists conditioned the bacteria with a chemical called 2,4-dinitrotoluene, or DNT, a volatile byproduct of trinitrotoluene, or TNT. Over time, DNT vapor seeps into the soil around the mine, and can be sniffed by bacteria.
Instead of roaming freely, the bacteria are immobilized in tiny gelatin-like particles to feed them while they’re active. Each bead, which is about 1 to 3 mm in diameter, contains about 150,000 active cells.
These latest genetically engineered bacteria are more responsive and sensitive than bacteria in the team’s previous field trials, says Dr. Belkin. And scientists no longer need to use laser signals to trigger the glow.
One key challenge the team is trying to overcome is to safely locate bioluminescent bacteria in an actual minefield. When they discovered the deposits, their light was so faint that the light from the moon, stars or nearby cities could drown out.
To help solve this problem, Aharon J. Agranat, a bioengineer at the Hebrew University, and other researchers reported in April in the journal Biosensors and Bioelectronics that they had developed a masking device. bacteria and detect their glow. The sensor system can then report its findings to a nearby computer, but it has not been tested outside of a lab environment.
The researchers also recently conducted field tests in Israel, working with the Israeli military to ensure the safety of the experiments, as well as an Israeli defense company. The results of these trials have not been published, but Dr Belkin calls them “generally very successful”.
In the future, the team hopes to use drones to deploy microbial sensors in a minefield, eliminating the need for humans to get close.
Dr. Burlage encountered another problem decades ago that the Hebrew University team grapples with even now: temperature. Israel’s microbial sensors only work from about 59 to 99 degrees Fahrenheit, meaning researchers will need to figure out how to adapt their system to scorching desert conditions.
The Israeli biotechnologists also admit that their microbial sensor could be used for both humanitarian and military purposes. DARPA, the Defense Advanced Research Projects Agency, contributed funding for their research.
However, microbial sensors for soil deposits exemplify 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. Technology, who was not involved in these studies.
“It is exciting and I hope to see these kinds of applications begin to move out of the lab and into the real world,” said Dr. Lu.