Researchers Lingchong You
and graduate student Cheemeng Tan have designed a set of experiments
on a living circuit created using genetically altered E.coli bacteria
that has demonstrated the existence
of "bistability" in bacteria cells. This bistability
makes some bacteria in the synthetic circuit act differently than the
other bacteria when stimulated in the same way.
the researchers, taking this ability for the bacteria to act
differently inside the circuit can greatly enhance the efficiency of
synthetic circuits. Synthetic circuits are being eyed for use in
treating disease conditions to produce proteins, enzymes, or
chemicals in a coordinated way. The circuits could also be used to
deliver drugs or selectively kill cancer cells according to the
The genetically altered bacteria used in
synthetic biology are altered to direct their actions in a way that a
software program directs a computer. The experiments by You and Tan
have shown that the genetic alteration (the software) can also
influence the bacteria (the computer).
"In the past,
synthetic biologists have often assumed that the components of the
circuit would act in a predictable fashion every time and that the
cells carrying the circuit would just serve as a passive reactor,"
You said. "In essence, they have taken a circuit-centric view
for the design and optimization process. This notion is helpful in
making the design process more convenient."
found that there can be unintended consequences that haven't been
appreciated before," said You. "In a population of
identical cells, some can act one way while others act in another.
However, this process appears to occur in a predictable manner, which
allows us to take into account this effect when we design
Electrical engineers have to deal with
bistability as well and in engineering, the term describes the
functioning of a toggle switch that can be on or off. During the
experiments conducted by the pair of researchers, they found that the
stimulation that turned the majority of the colony of E.coli on,
making them grow more slowly, also turned some of the bacteria off
making them grow faster.
"It is as if the colony received
the command not to expand too fast when the circuit is on," Tan
explained. "Now that we know that this occurs, we used computer
modeling to predict how many of the cells will go to the 'on' or
'off' state, which turns out to be consistent with experimental
The researchers believe that the discovery
can aid scientists and researchers in building more efficient
synthetic circuits in the future.