The sigma factor σB is required for the development of the growth phase-and temperature-dependent increases in thermoresistance and membrane rigidity in Staphylococcus aureus

The aim of this study is to determine the role that sigma(B) factor plays in the development of growth phase- and temperature-dependent thermoresistance in Staphylococcus aureus cells and its possible relationship with membrane fluidity. Cells of S. aureus strain Newman and its isogenic Delta sigB mutant (strain IK184) were grown at different temperatures to exponential and stationary growth phases, and the relationship between sigma(B) activity (estimated by RT-qPCR), heat resistance, and membrane fluidity (fatty acid profiles and DPH fluorescence anisotropy) was assessed. sigma(B) was required for the development of the growth phase- and temperature-dependent increases in thermoresistance and membrane rigidity (up to 37 degrees C), although a direct correlation between sigma(B) activity and heat resistance or membrane fluidity in S. aureus could not be established. Results obtained also revealed the existence of sigma(B)-independent growth phase and temperature (>37 degrees C) heat adaptation mechanisms. Moreover, it was demonstrated that sigma(B) does not control the fatty acid synthesis in S. aureus. Results obtained in this work contribute to a deeper knowledge of S. aureus physiology and to the development and design of more effective processes used by the food industry for microbial inactivation.