Typical temperature range for mesophilic microorganisms?

• A. -10 to 0°C
• B. 60-100°C
• C. 20-40°C (max 45°C)
• D. 0-10°C

Answer: (C)

Mesophiles are organisms that thrive at moderate, comfortable temperatures where their enzymes and membranes function best. Their growth typically occurs from about 20°C up to 40°C, with many species able to tolerate up to around 45°C. This range reflects a balance where metabolic processes run efficiently without the proteins denaturing or membrane integrity being compromised. Temperature outside this band disrupts enzyme activity or cellular structures: too cold and metabolism slows too much; too hot and proteins unfold and membranes destabilize. That’s why organisms adapted to human-associated environments and many soil and water ecosystems fit this middle range. In contrast, colder ranges are occupied by psychrophiles, and hotter ranges by thermophiles, so the 20–40°C (max ~45°C) window is the best match for mesophiles.