Redox potential changes in bacterial cultures under stress conditions

Oxidation/reduction potential (ORP, redox potential, or Eh) is one of the physicochemical parameters characterizing the state of microbial cultures. Changes in pH and concentration of the redoxactive gases (O2, H2, and H2S) in the cultivation medium are assumed to be the major factors of redox potential changes in the cultures of aerobic microorganisms. In the review, results of the studies of redox potential changes in various bacterial cultures under various stress conditions are summarized. The characteristic feature of these stress factors is the absence of direct correlation between the redox potential, on one hand, and partial oxygen pressure and pH, on the other. Extracellular low-molecular weight thiols (LWT) were demonstrated to be the major contributors to such changes in the redox potential. The possible role of the changes in LWT concentrations inside and outside the cells in the processes of signal transduction and redox regulation of cellular functions is discussed.