Extreme temperature exposure has negative demographic consequences for Sulfolobus acidocaldarius

Microorganisms inhabiting geothermal springs and volcanic systems experience fluctuating temperatures that can periodically exceed their upper thermal limits, but the demographic consequences of such exposure remain poorly understood. Here, we investigated demographic responses of the thermophilic archaeon Sulfolobus acidocaldarius to an extreme temperature (94.1{degrees}C) under two regimes: sustained exposure varying in duration, and episodic exposure interspersed with recovery at a permissive temperature (75{degrees}C). Under sustained exposure, populations showed no detectable loss of viability after 15 min but declined thereafter, decreasing by approximately five orders of magnitude after 120 min. Under episodic exposure, populations remained viable across nine exposure-recovery cycles but declined in density with successive cycles. Similar responses were observed for three strains, including a DNA mismatch repair knockout ({Delta}nucS), indicating that mismatch repair deficiency did not affect viability or recovery. Together, these results demonstrate that S. acidocaldarius can withstand brief and repeated exposure to near-boiling temperatures, with mortality determined primarily by cumulative exposure duration rather than a fixed thermal threshold.