Scientists from MIT wants to harness the energy produced by microbes found in mines, at the bottom of lakes, and even the human gut to produce electricity.

In a new paper, a team of scientists described a technique that can quickly analyze a small sample of bacteria and determine the specific property associated with its ability to produce energy. They hope to use the electricity generated from the microbe to clean sewage water.

The technique was published in the journal Science Advances.

Microbe Energy

Certain species of bacteria can survive even in the most extreme conditions. Some thrive in an environment where oxygen is scarce and, therefore, have to adapt by developing a form of breathing that involves excreting electrons. These are the types of microbes that the scientists of MIT need to produce energy.

However, the team still needs to pick which type of bacteria is up for the task.

"The vision is to pick out those strongest candidates to do the desirable tasks that humans want the cells to do," commented Qianru Wang, a postdoc at MIT and the first author of the study.

Growing bacteria in a lab setting is difficult, takes a lot of time, and can be very expensive. The new technique addresses these concerns by allowing scientists to probe only a small sample of microbes.

Dielectrophoresis

The team has been perfecting the technique for the past 10 years. They built microfluidic chips with small channels in which the microliter-samples of bacteria will flow. Each channel is pinched in the middle to produce an hourglass shape. By applying voltages in the pinched part of the channels, the scientists' aim is to separate cells based on their ability to produce electricity.

The process is called dielectrophoresis, which was previously used to separate cells from two very different sources, say birds and frogs. They used the same technique to separate and measure closely related cells.

During the experiment, the team of scientists flowed a microliter sample of bacteria through the microfluidic channel and slowly increased the voltage applied in the pinched section of the hourglass. They observed that the resulting electric field pushed the strains of bacteria forward until they reached the pinched area which repelled them, trapping them in place. Some bacteria were trapped at a lower voltage and some at a higher voltage.

The researchers took note of all the data from the experiment and calculated the cell's polarizability using a computer simulation. They found that strains of bacteria that are more electrochemically active also have higher polarizability.

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

Harnessing Electricity

Wang added that the technique can be used to gauge the ability of the strain of bacteria by measuring polarizability. Collaborators of the team are already in the process of trying the technique to test other strains of bacteria.

If successful, the technique can lead to clean energy, bioremediation, and production of biofuels.