All microorganisms have temperature ranges that determine growth. Overall, microorganisms are unique in their ability to exist and grow at temperatures ranging from 14 to 230°F (-10–110°C). Temperature restrictions are due to limitations in cell metabolism. A microorganism’s maximum temperature is the highest temperature at which growth can occur; minimum temperature is the lowest temperature at which growth can occur. A microorganism’s optimum temperature is the temperature at which the growth rate is the fastest. The maximum, minimum, and optimum temperatures define the range of growth for each microorganism and are collectively referred to as the cardinal temperatures.

Bacteria are often divided into four groups on the basis of their average temperatures for growth: psychrophiles, mesophiles, thermophiles, and extreme thermophiles (sometimes called extremophiles; see the chapter “Basics of Biology”). The following chart lists the temperature ranges at which these groups can grow: