Revealing metabolic storage processes in electrode respiring bacteria by differential electrochemical mass spectrometry.

In this work we employ differential electrochemical mass spectrometry (DEMS) in combination with static and dynamic electrochemical techniques for the study of metabolic processes of electrochemically active bacteria. CO2 production during acetate oxidation by electrode respiring bacteria was measured, in-vivo and online with a sensitivity of 6.5 ⋅ 10-13 mol/s. The correlation of ion current and electrical current provides insight into the interaction of metabolic processes and extra-cellular electron transfer. In low-turnover CVs, two competing potential dependent electron transfer mechanisms were observed and formal potentials of two redox systems that are involved in complete oxidation of acetate to CO2 were determined. By balancing charge and carbon flows during dynamic measurements, two significant storage mechanisms in electrochemically active bacteria were identified: 1) a charge storage mechanism that allows substrate oxidation to proceed at a constant rate despite of external current flowing in cathodic direction. 2) a carbon storage mechanism that allows the biofilm to take up acetate at an unchanged rate at very low potentials even though the oxidation to CO2 stops. These storage capabilities allow a limited decoupling of electrical current and CO2 production rate.