In Situ Spectroelectrochemical Investigation of Electrocatalytic Microbial Biofilms by Surface‐Enhanced Resonance Raman Spectroscopy

Abstract

A mixed‐culture‐derived microbial biofilm, grown on silver electrodes, was studied in vivo with surface‐enhanced resonance Raman scattering (SERRS) in combination with cyclic voltammetry. This experimental approach provides unprecedented structural information about the outer membrane cytochromes involved in the direct electron transfer across the bacterium–electrode interface.

Long-range electron transport in Geobacter sulfurreducens biofilms is redox gradient-driven

“…Here, only the set of microelectrode bands comprising electrode 1 was used to collect electrons resulting from acetate oxidation. The CV exhibits the sigmoid-shape dependency of steady state catalytic current on applied potential reported for full grown G. sulfurreducens biofilms (19,20,36), consistent with an electrode catalytic (EC) reaction scheme (61), in which a reactant (in this case, acetate) that cannot be directly oxidized by an electrode owing to poor kinetics is coupled to reduction of a redox cofactor that can be reversibly oxidized by an electrode, such as a ctype cytochrome (41). The negative deviation in current observed during the anodic scan of the experimental CV has been previously noted, and it is attributed to possible inhibition of acetate oxidation and/or possible accumulation of electrons in cells occurring at the end of the cathodic scan and beginning of the anodic scan, when the potential applied to electrode 1 was fairly negative (20).…”

“…Geobacter cells possess an abundance of multiheme c-type cytochromes on their outer membrane, in the ECM, and along PilApili (24)(25)(26)(27)(28)(29)(30)(31)(32)(33). Cyclic voltammetry (19,(34)(35)(36)(37) and spectroelectrochemical measurements (38)(39)(40)(41)(42)(43) of actively respiring Geobacter biofilms are consistent with long-range electron transport mediated by sequential electron transfer reactions through a network of bound redox cofactors comprised of ECM c-type cytochromes terminating with electron transfer to the anode surface. This proposed process, analogous to diffusive electron transport observed for redox polymers containing discrete redox moieties (20,(44)(45)(46)(47)(48), is an extension of the normal mode of electron transport in biological systems involving redox proteins (2) to longer length scales (up to 18 μm in the case of biofilms described here).…”

Waste Water Derived Electroactive Microbial Biofilms: Growth, Maintenance, and Basic Characterization

“…Especially the combination of CV and spectroscopic methods has provided unprecedented insights in the EET mechanisms and its molecular nature, e.g. 25,26 In parallel the theoretical framework for the extraction of thermodynamic and theoretical characteristics of the microbial EET was broadened and deepened [27][28][29][30] . In contrast, however, experimental mishandling or inadequate data-analysis often hamper the appropriate application of CV in the field of microbial bioelectrochemistry.…”

BioRock: new experiments and hardware to investigate microbe–mineral interactions in space

“…Biofilm structure: The effects of microgravity and Martian gravity on the biofilm structure will be studied using scanning electron microscopy (Hawser et al 1998), confocal microscopy (De Beer et al 1997), Raman spectroscopy (Millo et al 2011) and staining techniques. The structures of the biofilms will be compared between the organisms from the flight experiment and the ground controls, a comparison will also be carried of the biofilms formed by the different test organisms.…”