The reduction potentials of bacterial suspensions

Abstract

The reduction potentials of suspensions of Bact. coli and Bact. alkaligenes were measured (1) electrometrically (2) colorimetrically and (3) electro-metrically in the presence of indicators. A few measurements were also made with Cl. sporogenes. The two former, alone or with succinate, show a slow continuous fall of potential at the electrode, which never reaches a constant value. Glucose and formate induce more neg. potentials, which, with Bad. coli, soon reach min. values. The potentials were shown to be due to electromotively active molecules capable of passing through a collodion sac, and not to the bacteria themselves or bacteria plus adsorbed substances. The potentials recorded by indicators, although sometimes in fair agreement with the electrode values (Bad. coli), often bear no relation to the latter (Bad. alkaligenes and Cl. sporogenes). The electrode measurements in presence of appropriate dyes give values agreeing with those indicated by the colorimetric study. The methods involving the use of indicators merely measure the point at which the rates of oxidation and reduction of the dye are the same. On the other hand, measurements of the electrode potential without an appropriate indicator give no information beyond the fact that there are certain (diffusible) substances in the soln. which can affect the electrode. There is no correlation between the mode of life of the organism and the "reduction potential" measured by these methods. Bact. coli is a facultative anaerobe, Bact. alkaligenes a strict aerobe and Cl. sporogenes a strict anaerobe, but the reduction potentials show no correlative differences.