Swimming Bacteria Power Microscopic Gears

A system of two "engaged" microscopic gears rotating by bacteria in opposite directions

Andrey Sokolov
Materials Science Division
Argonne National Laboratory
Argonne, Illinois 60439
and
Department of Ecology and Evolutionary Biology
Princeton University
Princeton, New Jersey 08543

Mario M. Apodaca
Departments of Chemistry
Northwestern University
Evanston, IL 60208

Bartosz A. Grzybowski
Departments of Chemistry
and
Chemical and Biological Engineering
Northwestern University
Evanston, IL 60208

Igor S. Aranson
Materials Science Division
Argonne National Laboratory
Argonne, Illinois 60439
and
Engineering Sciences and Applied Mathematics
Northwestern University
Evanston, IL 60208

Two gears approximately 380 μm in diameter and 50 μm thick with asymmetric teeth were placed in suspensions of aerobic swimming bacteria Bacillus subtilis confined to thin, freestanding liquid film. Swimming bacteria moving randomly in a thin fluid film can rotate the gear. Whereas the gear’s center of mass exhibits apparent random motion, the gears are spun in the direction determined by the gear’s asymmetry, i.e. orientation of the teeth’s slanted edges.

Once two gears of opposite "chiralities" of the teeth are close to one another, the gears interdigitated their teeth and started rotating in synchrony, but in opposite directions. 

The rotation rate could be controlled by the flow of nitrogen/oxygen through the bacterial broth, since concentration of oxygen affects the swimming speed of bacteria. The concentration of bacteria was 2 × 10¹⁰ cm⁻³ and the film thickness was 200 μm.

References

Andrey Sokolov, Mario M. Apodaca, Bartosz A. Grzybowski, and Igor S. Aranson Swimming bacteria power microscopic gears PNAS 107, 969 (2010).

Usage Information

Reporters may freely use this image as long as they include the following credit: "Image courtesy of A. Sokolov/Princeton Univesity".

For further information, contact:
Jason Bardi
(301) 209-3091