The stress response is a metabolic program activated in response to unfavorable environmental factors. Various mechanisms are involved in its activation, depending on the type of stress factor and on the metabol- ic characteristics of the micro-organism. The stress response mechanisms occurring in bacteria are the gener- al stress response, the stringent response, the oxidative stress response, the TA system, and QS, which is a mechanism of response to population cell density. The end result of the activation of this program, which is resistance to the same stress factor or cross-resistance (i.e. resistance to other types of stress factors), depends on the interaction at various levels between different stress response mechanisms. The phenomenon of resis- tance is particularly important in the case of soil bacteria, which is often exposed to both natural and anthro- pogenic stress factors. The stress response determines such diverse microbial functions as survival in periods of starvation, adaptation to the presence of antibiotics, synthesis of antibiotic substances, interactions with a eukaryotic symbiont, and atmospheric oxygen fixation. At the ecosystem level, it helps to maintain climax conditions, i.e. a quantitatively and qualitatively stabilized community of micro-organisms in a given envi- ronment, which affects the biological activity of the soil.