Bacteria constitute a large domain of micrometer-long organisms that exist in different shapes ranging from rods, spheres, and spirals. Their potential could be harnessed in the future to provide a means for power.
When observed under a microscope, you'll notice that bacteria produces lots of random movements. This kind of movement has too much spontaneity and in itself cannot produce energy. Scientists admit that we won't be able to power homes with bacteria anytime soon. Even then it will be possible to power micromachines effectively in a short while.