Programmable "discharge" bacteria

When you hit your finger with a hammer, you immediately feel pain
.
You will react
immediately.
But what if the pain starts 20 minutes after the hit? By then, wounds may be more difficult to heal
.
Scientists and engineers at Rice University say the same is true of
the environment.
If chemical spills in the river go unnoticed within 20 minutes, it may be too late
to remedy.

Their bioelectronic sensors can help
.
Caroline Ajo-Franklin and Jonathan (Joff) Silberg, a team led by Rice synthetic biologists, developed engineered bacteria
that report a variety of contaminants.
Their study was published in Nature
.

Cells can be programmed to recognize chemical invaders and report
within minutes by releasing a detectable electric current.
According to the researchers, this "smart" device can power itself by removing energy from the environment to ensure water safety
when monitoring conditions in environments such as rivers, farms, industries and sewage treatment plants.
The environmental information transmitted by these self-replicating bacteria can be customized by replacing a protein in the eight-component synthetic electron transport chain, which produces a sensor signal
.

"I think this is the most complex protein real-time signaling pathway ever established," said
Silberg, director of the Rice Methodology, Synthesis, and Physical Biology PhD program.
"Simply put, imagine a wire that directs electrons from cellular chemicals to the electrode, but we break the middle part of the wire
.
When the target molecule hits, it reconnects and energizes the entire pathway
.
”

Ajo-Franklin said: "It's actually a miniature electronic switch
.
You put the probe in the water, measure the current, it's as simple
as that.
Our equipment is different because microorganisms
are encapsulated.
We don't release them into the environment
.
”

The researchers' proof-of-concept bacteria are E.
coli, and their first target is thiosulfate, a dichlorinating agent used in water treatment that causes algae blooms
.
In addition, there are convenient water sources to test: Galveston Beach, Brays in Houston, and the mouth
of the Buffalo River.

At first, they attached E.
coli to the
electrodes.
"They don't naturally attach to the electrodes," Ajo-Franklin said
.
"The strains we use don't form biofilms, so when we add water, they fall off
.
" When this happens, the electrodes transmit more noise than the signal
.

Working with Xu Zhang, a postdoctoral researcher in Ajo-Franklin's lab, they encapsulated the sensor in a lollipop-shaped agarose that allowed contaminants to enter but kept the sensor still and reduced noise
.

"Xu's background is in environmental engineering," Ajo-Franklin said
.
"She didn't come in and say, 'Oh, we have to fix biology
.
'" She said, 'What can we do with these materials?' Synthetic biology requires great, innovative work on materials to shine
.
”

With physical constraints in place, the lab first coded E.
coli to express a synthetic pathway
that generates an electric current only when it encounters thiosulfate.
This live sensor is able to sense the chemical at levels below 0.
25 millimoles per liter, well below levels
that are toxic to fish.

In another experiment, E.
coli was recoded to sense an endocrine disruptor
.
The signal is greatly enhanced
when the custom-synthesized conductive nanoparticles are wrapped in cells in agarose lollipops.
The researchers report that these encapsulated sensors detect this contaminant 10 times
faster than previous state-of-the-art devices.

Silberg says the complexity of this design extends far beyond the signal path
.
"This chain has eight components that control the flow of electrons, but there are other components that make up the wires that connect the
molecules," he said.
There are 12 semi-components and nearly 30 metal or organic cofactors
.
This thing is huge
compared to our mitochondrial respiratory chain.
”

Silberg said he believes engineered microbes could perform many tasks in the future, from monitoring gut microbiota to sensing contaminants such as viruses, building
on successful strategies for detecting SARS-CoV-19 at wastewater treatment plants during the pandemic.

"For those instantaneous pulses, real-time monitoring becomes very important," he said
.
"Because we grow these sensors, they can be quite inexpensive
to manufacture.
"

To that end, the team is working with Rafael Verduzco, a professor of chemical and biomolecular engineering, materials science and nanoengineering at Rice University, who recently led a $2 million National Science Foundation grant to develop real-time wastewater monitoring
with Ajo-Franklin, Silberg, biological scientist Kirstin Matthews, and civil and environmental engineer Lauren Stadler.

Real-time environmental monitoring of contaminants using living electronic sensors