Which temperature-based category would you expect to find in hot springs and volcanic environments?

• A. Hyperthermophiles
• B. Psychrophiles
• C. Mesophiles
• D. Thermophiles

Answer: (D)

Temperature is the controlling factor for which microbes can thrive in hot springs and volcanic environments. In these settings the high heat selects for organisms that grow best at elevated temperatures, known as thermophiles. They typically have optimum growth in the range of about 45°C to 80°C and possess heat-stable enzymes and membranes that remain intact and functional under heat. While some extreme cases near vents can host hyperthermophiles that tolerate even higher temperatures, the common expectation for hot springs is thermophiles. Psychrophiles prefer cold conditions, mesophiles favor moderate temperatures, and hyperthermophiles occupy the most extreme heat (often beyond typical hot springs), so thermophiles are the best fit for these environments.