Heat-adaptation induced thermotolerance in Staphylococcus aureus: Influence of the alternative factor σ

The role of σ^B in the Staphylococcus aureus heat-shock induced thermotolerance was investigated. Survival curves at 58 °C of S. aureus strain Newman and its isogenic ΔsigB mutant were obtained for native and heat-shocked cells (45 °C for 5–120 min) in exponential and stationary phase of growth. The magnitude of the acquisition of thermotolerance at 58 °C depended on the growth phase and on the duration of the heat shock. Stationary growth phase cells were always more heat tolerant than exponentially growing cells and thermotolerance increased with heat-shock duration up to 120 min. S. aureus cells were able to increase their heat tolerance in the absence of the σ^B factor. In stationary phase, whereas in the parental strain the thermotolerance was increased by a factor of 12 after a heat shock of 120 min at 45 °C (δ values at 58 °C for native and heat-shocked cells were 0.63 and 7.22 min, respectively), in the mutant strain it increased 43 fold (δ values 0.09 and 3.87 min). The addition of chloramphenicol to the adaptation medium resulted in a lower increase in heat tolerance but did not prevent it completely, suggesting that S. aureus can partially increase its thermotolerance without “de novo” protein synthesis. Both the number of non-damaged cells and the proportion of cells able to repair sublethal damage were higher for heat-shocked cells.