Varies tremendously - Microbes are ubiquitous meaning they are everywhere. There is not an ecological niche anywhere, including Mars, it seems, that some microbe has not found a way to live. Bacteria or the procaryotes seem to be the most versatile group of microbes at exploiting both hospitable and seemingly inhospitable environments. All microbes have a pH range they prefer and another range they can tolerate.
SOme bacteria have a narrower range than others.
Could burst the cell if equalized. Permeases in cell membrane keep it out and the cell wall helps to. Why salt is a preservative. Kills bacteria by dehydrating them. V. Oxygen - Bacteria vary in their oxygen requirement and tolerance.