New experimental techniques and protocols are needed to study microbiologically influenced corrosion (MIC). In this work, we studied the capacity of microorganisms to modify their environment in vitro. The methodology involved cyclic voltammetry measurements using carbon electrodes modified with cobalt phthalocyanine, which is a known catalyst for the two-electron reduction of O-2 to give peroxide. MuellerHinton (21 g/L) was used as an electrolyte in a sterilized aqueous medium. The open circuit potential (OCP) and oxygen concentration behaved similarly over time, with generally similar growth curves. However, there were peculiarities that indicated the presence of peroxide and catalase. Catalase activity was demonstrated by comparing the voltammetric responses of the culture medium in the absence and presence of bacterial strains of Escherichia coli (Gram thorn) and Staphylococcus aureus (Gram-), both facultative and catalase positive. With this system, which is capable of discriminating O-2 and hydrogen peroxide, catalase activity is highly evident, and at its maximum at the end of the exponential stage of the growth curve. (C) 2019 Published by Elsevier Ltd.