As part of an experiment called BioRock, there are three different types of microbes currently aboard the ISS slowly eating away at rocks in order to extract useful metals from them.
The practice of biomining is already used here on Earth for metals such as copper and gold, but before biomining can take place in space scientists must determine how different strengths of gravity affect how the microbes grow and extract metals.
Aboard the ISS, some microbes experience microgravity which is what they would feel if they were to be used on an asteroid. Other microbes experience simulated Martian gravity with the hope that they can someday be used on Mars.
If humans ever want to settle on the Moon, Mars, or any other celestial body, they will most likely have to extract materials from that body rather than bring them from Earth. Microbes could do the work of extracting materials or making soil for us while we focus on more important and complex duties.
One of the microbes, S. desiccabilis, handled microgravity rather well, however, the other two did not. Nevertheless, there is another experiment called BioAsteroid set to launch in December. Humans are still years away from establishing a serious presence on another celestial body, so we have the opportunity to perfect our microbes in the meantime.