Motion of Bacteria to Power Micro Machines?

In spite of all that is bad about them, bacteria are rapidly expanding their range of usefulness to mankind thanks to green technology!

A quite interesting discovery will be the subject of this article and it was made by a scientist from Princeton University and a group of researchers from the U.S. Department of Energy’s (DOE) Argonne National Laboratory and Northwestern University.

The discovery?

That common bacteria when suspended in solution can be utilized to ‘turn microgears,’ in order to generate mechanical energy!

Microgears? Never heard of them before?

These are infinitesimally small structures that can be immersed in solution along with the bacteria. You can see in the diagram below what they look like. They have slanted spokes around them. They have a diameter of about 400 microns and a thickness of about 50 microns. However even at such dimensions they are still about a million times bigger than the bacteria!

Silhouettes of several gear designs. (Courtesy: Igor Aronson / Argonne National Laboratory. )

So how does this work?

The microgears are placed in solution together with the bacteria. A common aerobic bacteria is used for this purpose: Bacillus subtilis. The bacteria then swim randomly in the solution occasionally colliding with the spokes on the microgears. What happens then? The microgears start to turn in one direction!

Diagram tracking the movement of gears turned by the bacteria (Courtesy: Igor Aronson / Argonne National Laboratory.)

A few hundred bacteria need to be employed to turn one microgear or wheel in this manner.

The motion of these microgears can then be harnessed to generate power.

How much power?

A very small amount, of the order of about a femtowatt. This is of course way too small to power any macroscopic machine. However… the technique can be used to power submillimeter objects or to operate the movable parts of microfluidic devices.

There’s more…

The speed at which the gears turn can also be controlled. How? By manipulating the oxygen supply to the suspended liquid. Being biological organisms, bacteria need oxygen to move. So can you guess what happens when the O₂ supply is limited? The bacteria will slow down of course. No second guesses then for what happens when O₂ supply is increased…