Blinking Bacteria As Biological Sensors

You’re probably aware that making lab organisms – or at least parts of them – glow a certain colour is relatively commonplace. Biologists frequently attach the gene for green fluorescent protein (GFP) or its differently coloured family members to a gene that they’re interested in, so whenever the gene of interest is activated GFP is produced and the relevant target fluoresces, a nice visible marker. 

In the last few years a group of researchers found a way of tying fluorescence to the cycle of bacteria’s biological clocks, producing rhythmic blinking. Last year they managed to coordinate this blinking in large groups of bacteria, which they compare to living neon signs. Now, they’ve shown that this system can be used as a living sensor for environmental pollutants.

From ScienceDaily:

Using the same method to create the flashing signs, the researchers engineered a simple bacterial sensor capable of detecting low levels of arsenic. In this biological sensor, decreases in the frequency of the oscillations of the cells’ blinking pattern indicate the presence and amount of the arsenic poison.

Because bacteria are sensitive to many kinds of environmental pollutants and organisms, the scientists believe this approach could also be used to design low cost bacterial biosensors capable of detecting an array of heavy metal pollutants and disease-causing organisms. And because the sensor is composed of living organisms, it can respond to changes in the presence or amount of the toxins over time unlike many chemical sensors.

“These kinds of living sensors are intriguing as they can serve to continuously monitor a given sample over long periods of time, whereas most detection kits are used for a one-time measurement,” said Jeff Hasty, a professor of biology and bioengineering at UC San Diego who headed the research team in the university’s Division of Biological Sciences and BioCircuits Institute. “Because the bacteria respond in different ways to different concentrations by varying the frequency of their blinking pattern, they can provide a continual update on how dangerous a toxin or pathogen is at any one time.”

They go on to explain that there are too many bacteria on their “microfluidic chips” (up to 60 million cells) for the bacteria to all coordinate in their usual way, which is called quorum sensing (roughly, relaying signaling molecules between them). They found, though, that colonies released gases that could be used to coordinate between them, while cells within colonies still coordinated by quorum sensing.

This is a pretty interesting idea. I trust biologists to be able to make bacteria sensitive to various molecules and react in various ways; I see no reason why bacteria wouldn’t be able to glow different colours based on the environment, for example. There may be more possibilities with living versus non-living sensors simply because of the incredible complexity of living things, which we can take advantage of without reconstructing from the ground up.

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