Heat Stress and Stringent Response
Bacteria have evolved complex and diverse regulatory networks to sense and respond to changes in the environment, including physical stresses such as heat or oxidative stress. These cellular stresses can lead to the unfolding and aggregation of proteins, which can also be sensed by heat shock response systems, allowing an appropriate cellular stress response. The universally conserved protein quality control system comprises a conserved set of chaperones and protease systems that monitor and maintain protein homeostasis. The cellular response to such protein unfolding stresses includes the induction of the expression of genes encoding these chaperones and proteases of the quality control system, also known as heat shock proteins.
At the same time, a second different type of cellular stress response system, which allows to limit and modulate translation, was observed. Thereby the protein load on the quality control system during heat or oxidative stress can be reduced. In Gram-positive bacteria, this response can be mediated for example by the oxidative and heat stress transcription factor Spx together with the stringent control second messenger and alarmone (p)ppGpp. These distinct and different stress response systems are both very important for the success and survival of bacteria in their environment, which includes pathogenic bacteria, that are challenged by the immune system during infection.