Charge accumulation and electron transfer kinetics in Geobacter sufurreducens biofilms

BONANNI, PABLO SEBASTIAN; SCHROTT, GERMÁN DAVID; ROBUSCHI, LUCIANA; BUSALMEN, JUAN PABLO

ENERGY & ENVIRONMENTAL SCIENCE

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2012 vol. 5 p. 6188 - 6195

1754-5692

Electroactive bacteria can use a polarized electrode as final electron acceptor, allowing the use of electrochemical techniques for a very accurate quantification of its respiration rate. Biofilm cell respiration has been recently demonstrated to continue after the interruption of electrode polarization since these bacteria can store electrons in the haemgroups of exocytoplasmic cytochromes. Interestingly, it has been shown that when the electrode is connected again, stored electrons can be recovered as a current superimposed to the basal steady state current produced by biofilm respiration. This work presents a model for the biofilm-catalysed electron transfer mechanism that reproduces the current profile obtained upon electrode reconnection. Themodel allows the estimation of kinetic parameters forinternalization of the reduced substrate by the cells and the subsequent reduction of cell internal cytochromes, the electron transfer to mediators in the exterior of the cell, charge transport across the biofilm matrix to the electrode through fixedmediators and, finally, the oxidation of cytochromes at the biofilm/electrode interface. Based on these estimates, the distribution of stored charge within the biofilm can also be calculated. The results indicate that the processes involved in electron transfer from acetate to internal cytochromes represent themain limitation to current production, showing that both electron transport through the matrix of cytochromes and interfacial electron transfer are orders of magnitudefaster than this process. Stored charge, on the other hand, is an order ofmagnitude higher inside the cells compared with that in the conductive matrix, suggesting that internal  cytochromes are approximately ten times more abundant inside the cells than in the conductive matrix.