Engineered bacteria could be used to detect water pollutants
Image credit: Brandon Martin/Rice University
Cells in Escherichia coli have been reprogrammed by Rice University researchers to release an electrical current that can sense pollutants in water within minutes.
The team behind the research believes that living biometric sensors could be the key to quickly reporting the presence of a variety of contaminants in the water supply and alert about possible environmental catastrophes – such as chemical spills – before they escalate.
The cells used in the study belonged to Escherichia coli (e.coli) – a type of bacteria found in the environment, foods, and intestines of people and animals – to release an electrical current that can sense pollutants quicker than traditional methods.
When detecting water contamination, timing is vital. Scientists have pointed out that chemical spills in rivers that go unnoticed for 20 minutes are incredibly difficult to remediate, so a tool like theirs could have a significant impact on the environment.
“A lot of times there are environmental contaminants that are accidentally released," said Caroline Ajo-Franklin, a professor of biosciences at Rice University. “If you could know quickly that they were being released then you could do something about it.”
She added: “The question is: can you sense your contaminants quickly so that you can stop them from having that detrimental impact?"
In an article published in Nature, the team described how cells can be programmed to identify chemical invaders and report within minutes by releasing a detectable electrical current.
The sensor is shaped like a lollipop and made up of engineered e.coli, attached to electrodes and encapsulated in a biofilm made from red seaweed.
The ‘smart’ devices could power themselves by scavenging energy in the environment as they monitor conditions in settings like rivers, farms, industry and wastewater treatment plants and to ensure water security, according to the researchers.
“It’s literally a miniature electrical switch,” Ajo-Franklin said. “You put the probes into the water and measure the current. It’s that simple. Our devices are different because the microbes are encapsulated. We’re not releasing them into the environment.”
The first chemical the team targeted was thiosulfate, a dichlorination agent used in water treatment that can cause algae blooms. The living sensor was able to sense this chemical at levels less than 0.25 millimoles per litre – far lower than levels toxic to fish, the researchers said.
Moreover, the system was also able to detect another chemical that is known to affect the human endocrine system up to 10 times faster than the previous state-of-the-art devices.
“I think it’s the most complex protein pathway for real-time signalling that has been built to date,” said Silberg, director of Rice’s Systems, Synthetic and Physical Biology PhD. Program.
“To put it simply, imagine a wire that directs electrons to flow from a cellular chemical to an electrode, but we’ve broken the wire in the middle. When the target molecule hits, it reconnects and electrifies the full pathway.”
The sensor is still in its proof-of-concept stage, but the team said the findings could help ensure water security in the future.
Silberg also said he sees engineered microbes performing many tasks in the future, from monitoring the gut microbiome to sensing contaminants like viruses, improving upon the successful strategy of testing wastewater plants for SARS-CoV-19 during the pandemic.
In July 2022, a University of Portsmouth study revealed that the UK’s wastewater infrastructure is increasingly vulnerable to “pollution events” due to climate change.
That same month, the UK's Environment Agency's annual assessment found an increase in polluting activities from most of England’s water and sewage companies, with performance on pollution falling to its lowest level since 2013.
In light of the “appalling” situation, the regulator called for the organisations’ executives to face prison time if they oversee serious and repeated pollution incidents.
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