Scientists engineer sound-reflecting bacteria
Internal imaging might be revolutionised by living ultrasound signallers. Andrew Masterson reports.
Scientists at the California Institute of Technology in the US have genetically engineered bacteria capable of sending sonar signals from deep within the human body.
The modified Escherichia coli contain genes from two other species of bacteria, enabling them to grow new internal structures called gas vesicles. The vesicles – used by some water-dwelling microbes to regulate buoyancy – can reflect ultrasound signals beamed in by medicos, revealing their precise location.
The GM E.coli, as reported in the journal Nature, potentially have many uses, including providing a signalling mechanism to allow doctors to determine whether certain drugs or other treatments are reaching optimum locations.
Researchers led by Mikhail Shapiro and Raymond Bourdeau started looking into the potential of bacteria as living soundboards more than six years ago. They were seeking solutions to a key problem in medical diagnosis: the depth and density of the human body is such that light-based imaging techniques are defeated at all but the shallowest insertions.
Ultrasound, they reasoned, is able to penetrate much more deeply. If it could be bounced off target bacteria, then precise locations could be identified and treatments modified in response to the data.
The team decided to use E.coli as the basis for the project.
“We wanted to teach the E. coli bacteria to make the gas vesicles themselves," says Shapiro. “I've been wanting to do this ever since we realised the potential of gas vesicles, but we hit some roadblocks along the way.”
The researchers’ first attempt involved extracting the genes responsible for gas vesicles from a species of cyanobacteria called Anabaena flos-aquae and inserting them into the E.coli genome. Nothing happened.
Undaunted, they next performed the same trick using genes from a more closely related species, Bacillus megaterium. This time, the E.coli did develop vesicles, but they were so small they were unable to reflect soundwaves.
Eventually, the team hit on a solution, by combining genes from both types of donor microbe. Bourdeau likens the result to a construction site.
“Essentially, we figured out that we need the bricks from Anabaena flos-aquae and the cranes from Bacillus megaterium in order for the E. coli to be able to make gas vesicles,” he says.
The scientists predict that very soon they will make the genetic engineering tech available for researchers who want to test the new bacteria in animals. Human trials are expected to be several years away.