Bacteria can be divided into three groups based on heat tolerance.
1. Psychrophilic: Bacteria that survive at low temperature are called Psychrophilic bacteria. All these bacteria can survive at or below zero temperature. A temperature of 25-300C is best for their best growth. For example- Psychrobacter, Acinetobacter, Arthrobacter, Pseudomonas.
2. Mesophilic: Bacteria that survive at normal temperature are called Mesophilic bacteria. A temperature of 30-40 0C is best for their best growth. Such as Azotobacter, Rhizobium.
3. Thermophilic: Bacteria that survive at high temperatures are called thermophilic bacteria. A temperature of 45-600C is best for their best growth. For example – Thermus aquaticus, Bacillus coagulans.