SPECIFIC AND GENERAL STRESS RESPONSES IN BACTERIA

In their unicellular state, bacteria are directly exposed to frequent and sometimes dramatic changes in an environment. The only way to survive and, if possible, to grow and multiply, is to adapt to these changes. Thus, being exposed to stressful conditions is the normal way of life for bacteria. Sometimes adaptation involves global changes in gene expression, which have made stress responses the paradigm of global gene regulation (130).

The necessity to adapt to environmental stresses applies to nonpathogenic and pathogenic bacteria alike. However, for a pathogen, stress responses are also crucial for coping with specific host-inflicted stress situations once the pathogen has entered the host organism. From the perspective of the pathogen, various host tissues or cellular compartments are characterized by different stress conditions. Therefore, a pathogen can also use its ability to sense environmental stresses as a guidance system and as a device to prepare in good time for upcoming stresses in its journey through the host organism.

In principle, two types of stress response have to be distinguished in bacteria: stress-specific responses and the general stress response. The numerous specific responses are induced by defined single-stress conditions, such as certain reactive oxygen species or specific DNA damage. The physiological function of these responses is to cope with the actual stress situation only. This may include elimination of the stress agent as well as repair of damage that has already occurred.