Scientists at the Massachusetts Institute of Technology (MIT) have developed a novel microfluidic technique that, they claim, can differentiate electricity-producing bacteria from other types of bacteria.
The process, they suggest, might one day open up the possibility of using the bacteria to produce 'clean' electricity.
There are different types of bacteria that can produce electricity, and some do it more efficiently than others. Such microbes usually exist in extreme, oxygen-deprived environments, such as at the bottom of lakes, in deep mines, and even in the human gut.
These micro-organisms have evolved a distinctive form of breathing which involves pumping out electrons from cells through tiny channels in cell membranes. Because of this unique characteristic, they become capable of producing electricity.
Scientists believe that these microbes could one day be harnessed to produce clean energy. At the moment, researchers are currently exploring ways to harness such bacteria to run fuel cells and to clean sewage water, among other potential applications. But a major challenge is that they are difficult to grow in labs.
In the past, scientists have used a dielectrophoresis process to separate the two kinds of bacteria based on their electrical properties. Now, MIT researchers claim to have developed a new technique enabling them to separate bacterial cells based on their ability to produce electricity.
In the study, researchers used an hourglass-shaped microfluidic channel to compare various strains of bacteria, each with a characteristic electrochemical activity. The team flowed microlitre samples of each strain through the channel, and then slowly increased the voltage across the channel - just one volt per second, from 0 to 80 volts.
Researchers then used a particle-image velocimetry technique to observe the activity of bacterial strains in the channel.
They observed that the bacterial cells initially propelled through the channel and eventually arrived at the pinched section, where they experienced a much stronger electric field. The team found that some bacteria were trapped in the channel at much lower voltages, while others were trapped at higher voltages.
Researchers measured the "trapping voltage" and cell size for each strain and then used a computer simulation to calculate the 'polarisability' for different strains. Polarisability refers to the property which indicates how easy it is for a cell to produce electricity in an electric field.
The team found that the bacteria which were more electrochemically active tended to have a higher polarisability.
"We have the necessary evidence to see that there's a strong correlation between polarisability and electrochemical activity," says Qianru Wang, a post-doctorate student in MIT's Department of Mechanical Engineering.
"In fact, polarisability might be something we could use as a proxy to select microorganisms with high electrochemical activity."
The findings of the study are published in journal Science Advances.
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