Thermophiles exist in temperatures above 50 o C, and include the extremophiles of archeobacteria. One of the functions of the prokaryotic cell wall is to keep the cell from bursting in hypotonic environments. In the opposite extreme, hypertonic solutions cause water to leave the cell, drying the cell out to the point of interfering with metabolism. It is difficult for most microorganisms to survive a strong hypertonic environments. Bacteria that can exist in salty environments are called halophiles .
Obligate aerobes require oxygen.
Facultative anaerobes grow well in oxygen, but can also grow without oxygen using the fermentation pathways. Obligate anaerobes grow without oxygen, and are harmed in the presence of it. Aerotolerant anaerobes cannot use oxygen for growth but will tolerate it. Microaerophilic organisms grow in oxygen levels lower than that of the air. Due to their small size, this process is difficult to observe.