Technique Identifies Electricity-Producing Bacteria

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In their new study, the researchers used their microfluidic setup to compare various strains of bacteria, each with a different, known electrochemical activity. The strains included  a “wild-type” or natural strain of bacteria that actively produces electricity in microbial fuel cells, and several strains that the researchers had genetically engineered. In general, the team aimed to see whether there was a correlation between a bacteria’s electrical ability and how it behaves in a microfluidic device under a dielectrophoretic force.

The team flowed very small, microliter samples of each bacterial strain through the hourglass-shaped microfluidic channel and slowly amped up the voltage across the channel, one volt per second, from 0 to 80 volts. Through an imaging technique known as particle image velocimetry, they observed that the resulting electric field propelled bacterial cells through the channel until they approached the pinched section, where the much stronger field acted to push back on the bacteria via dielectrophoresis and trap them in place.

Some bacteria were trapped at lower applied voltages, and others at higher voltages. Wang took note of the “trapping voltage” for each bacterial cell, measured their cell sizes,  and then used a computer simulation to calculate a cell’s polarizability — how easy it is for a cell to form electric dipoles in response to an external electric field. 

From her calculations, Wang discovered that bacteria that were more electrochemically active tended to have a higher polarizability. She observed this correlation across all species of bacteria that the group tested.

“We have the necessary evidence to see that there’s a strong correlation between polarizability and electrochemical activity,” Wang says. “In fact, polarizability might be something we could use as a proxy to select microorganisms with high electrochemical activity.”

Wang says that, at least for the strains they measured, researchers can gauge their electricity production by measuring their polarizability — something that the group can easily, efficiently, and nondestructively track using their microfluidic technique.

Collaborators on the team are currently using the method to test new strains of bacteria that have recently been identified as potential electricity producers.

“If the same trend of correlation stands for those newer strains, then this technique can have a broader application, in clean energy generation, bioremediation, and biofuels production,” Wang says.

This research was supported in part by the National Science Foundation, and the Institute for Collaborative Biotechnologies, through a grant from the U.S. Army.

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