Application of redox indicators for measuring redox potential in growing cultures of microorganisms

A colorimetric method for quantitative measurement of the oxidation/reduction potential (ORP) in liquid and agar media was developed. The range of 12 dyes (redox indicators) to measure the ORP in growing cultures in the range from -30 to -420 mV was established. The method allows measuring the rate of ORP decrease without depressurizing the cultivator in a liquid medium, and stereometric characterize the distribution of redox zones in liquid or agar media. A possibility of using two dyes to determine the rate of ORP change in the growing culture of hydrogen-producing bacteria, two strains of genus Bacillus and Escherichia coli 926 (ATCC 8789) was shown. Stereometric configuration of redox zones in the layer of liquid medium is determined that bacteria sorbed on the substrate and locally decrease the ORP. Culture’s age affects the speed of ORP decrease. At using of 1-day culture, the speed of ORP decrease in liquid medium was 2–3 times higher than at using 3-day culture. During growth of aerobic and facultative anaerobic bacteria, ORP decreased on the surface of agar media to Eh ≤ -100 mV under the streak or colony, and to Eh ≤ -50...-90 mV – in the area of 4–9 mm from the edge of streak or colony