Which temperature range corresponds to mesophilic bacteria?

• A. < 68
• B. 0 to 32
• C. 68 to 113
• D. > 113

Answer: (C)

Mesophilic bacteria grow best at moderate temperatures, roughly 20–45°C, which is about 68–113°F. At these temperatures enzymes function efficiently and cell membranes remain properly fluid, allowing steady metabolism and growth. That’s why the range 68–113°F is the mesophile range. Temperatures below 68°F are generally too cool for most mesophiles (psychrophiles dominate colder environments), while temperatures above 113°F are too hot (thermophiles take over). In wastewater treatment, mesophiles are common workhorses under typical process temperatures, driving organic matter breakdown.