(Phys.org)—When researchers deposit a drop of fluid containing thousands of free-swimming, genetically engineered E. coli onto an array of micromotors, within minutes the micromotors begin rotating. Some of the individual bacteria have swum head-first into one of the 15 microchambers etched on the outer edge of each micromotor, and with their flagella protruding outside the microchambers, together the swimming bacteria cause the micromotors to rotate, somewhat similar to how a flowing river rotates a watermill.