Microbes living in extremely dry conditions have it tough. Water is important both for the chemistry and structure of all cells. Desert microbes are very good at acquiring and holding on to the water they can find, but in places such as the Atacama Desert in Chile, there's almost none available.
However, microbes can be very resourceful. In this study, phototrophs were discovered that can actually extract water molecules bound up in the crystalline structure of the mineral gypsum, and this allows them to survive in hyperarid regions. They do this by secreting organic acid molecules to etch the rock and release the water, converting gypsum to anhydrite, which is a mineral with the same chemical structure except without the water.