Well known bacteria, such as Escherichia coli and Bacillus subtilis, which are classified as mesophiles, grow rapidly at “moderate” temperatures ranging from 30 to 37ºC and cannot grow over 50ºC. Bacteria which can grow above 50ºC are called thermophiles. Thermophiles that can also grow below 50ºC are called moderate thermophiles (or facultative thermophiles). Thermophiles that can grow only above 50ºC are called extreme thermophiles (or obligate thermophiles). In particular, extreme thermophiles whose optimum growth temperatures are more than 80ºC are called hyperthermophiles.
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