Charge accumulation and electron transfer kinetics in Geobacter sulfurreducens biofilms

PABLO SEBASTIÁN BONANNI; GERMÁN DAVID SCHROTT; LUCIANA ROBUSCHI; JUAN PABLO BUSALMEN

ENERGY & ENVIRONMENTAL SCIENCE

ROYAL SOC CHEMISTRY

Año: 2012 vol. 5 p. 6188 - 6195

1754-5692

Electroactive bacteria can use a polarized electrode as final electron acceptor, allowing the use ofelectrochemical techniques for a very accurate quantification of its respiration rate. Biofilm cellrespiration has been recently demonstrated to continue after the interruption of electrode polarizationsince these bacteria can store electrons in the haem groups of exocytoplasmic cytochromes. Interestingly,it has been shown that when the electrode is connected again, stored electrons can be recovered asa current superimposed to the basal steady state current produced by biofilm respiration. This workpresents a model for the biofilm-catalysed electron transfer mechanism that reproduces the currentprofile obtained upon electrode reconnection. The model allows the estimation of kinetic parameters forinternalization of the reduced substrate by the cells and the subsequent reduction of cell internalcytochromes, the electron transfer to mediators in the exterior of the cell, charge transport across thebiofilm matrix to the electrode through fixed mediators and, finally, the oxidation of cytochromes at thebiofilm/electrode interface. Based on these estimates, the distribution of stored charge within the biofilmcan also be calculated. The results indicate that the processes involved in electron transfer from acetateto internal cytochromes represent the main limitation to current production, showing that both electrontransport 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 of magnitude higher inside the cellscompared with that in the conductive matrix, suggesting that internal cytochromes are approximatelyten times more abundant inside the cells than in the conductive matrix.