Grey Goo - Ecophage Apocalypse!

Here, it is described that a tiny nanomachine (notice I added "nano" to machine to make this seem more exciting) has been built that can emit electronic pulses that then steer bacteria.

On such a small device there is little room for batteries, sensors or transmitters. So the solar cell on top delivers power, sending an electric current to both a sensor and a communication circuit. The communication component sends tiny electromagnetic pulses that are detected by an external computer. The sensor meanwhile detects surrounding pH levels–the higher the pH concentration, the faster the electromagnetic pulses emitted by the micro-machine.

The external computer uses these signals to direct a swarm of about 3,000 magnetically-sensitive bacteria, which push the micro-machine around as it pulses. The bacteria push the micro-machine closer to the higher pH concentrations and change its direction if it pulses too slowly. This is more practical than trying to attach the bacteria onto the micro-machines, says Martel, since the bacteria only have a lifespan of a few hours. “It’s like having a propulsion engine on demand,” he says.

This is all well and good until the robots start replicating.

In Science Fiction (and in science, but less popularly so) there is a term called Grey Goo. The fundamental idea is this: if someone were to create a tiny little autonomous robot whose function was simply to replicate itself as many times as possible, as fast as possible, using whatever materials are nearby, then the robot could consume the earth in 6 days.
The math is fairly simple: 2^X = Armageddon, where X is the time it takes to consume the earth.
X is somewhere between 3 and 6 days, depending on the machine's replication time. Ideally, you want the machine to replicate once a minute.

The term grey goo comes from "Earth, when viewed from space, had been reduced to a spherical blob of grey goo" in the original incarnation. I don't want to delve on this, other than to say that it's highly implausible, considering the high temperatures found at the center of the earth.

What I do want to point out is that using machines to create bacterial propulsion is very novel and very pointless.

And what about my great idea to seed Mars with genetically modified thermophilic bacteria from hot springs under the ocean floor.

Build a bacteria that takes iron oxide and reduces it to pure iron while releasing oxygen (O2) and ozone (O3). The bacteria would use solar energy as its reducing mechanism. The bacteria would slowly blanket Mars via windstorms, cleaning the surface of the planet of its rusty colored dust, while filling the atmosphere with oxygen and ozone, thickening the atmosphere and preparing it for human colonists.
Simultaneously, deep space probes would be used to steer comets at Mars, peppering it's surface with water. Mars polar ice caps would melt. In 50 or 100 years, the planet could be basically habitable. And equipment used on Mars to build colonies would never rust, courtesy the rust-eating bacteria used to terraform the planet.