Respiratory Au nucleation and microelectrode techniques reveal key features of bacterial conductive matrix

ORDÓÑEZ, MARÍA VICTORIA; ROBUSCHI, LUCIANA; HOPPE, CRISTINA ELENA; BUSALMEN, JUAN PABLO

Environmental Science: Nano

Royal Society of Chemistry

Lugar: Londres; Año: 2020 vol. 7 p. 3189 - 3200

2051-8153

The previously reported relay network conductivity model has shed some light on the structure andmechanisms behind long-distance extracellular electron transfer (EET) in Geobacter biofilms. Thestructuration of c-type cytochromes (c-Cyt) in supramolecular complexes and their interactions with pili,as a requirement for achieving external intermolecular ET, were put forward. Such an arrangementsupports a redox gradient-driven process limited by potential loss along the biofilm, which ultimately limitstechnological developments on bioanodes. Geobacter cells display wide respiratory versatility, includinguranium, palladium, silver and gold salt reduction, which often yields nanoparticles (NPs). Here, we tookadvantage of the ability of G. sulfurreducens to produce monodisperse AuNPs (G.Au) to interpret andimprove the EET mechanism. Both metabolic stratification and co-localization of c-Cyt and AuNPs wereanalyzed by TEM microscopy and Raman spectroscopy to evaluate the relation between these elementsand reveal the spatial organization of redox proteins, giving support to the 2-fold increase in the currentdensity production that was measured as a consequence of improving cell connectivity with goldnucleation. The final corroboration of specific interactions between AuNPs and c-Cyt came from theelectrophoretic analysis of the nanostructure isolated fractions. We observed that electrons accumulated inthe absence of polarization reduced Au(III) throughout the biofilm and can also be drained through a poisedmicroelectrode located at 100 μm from the basal electrode used for biofilm growth, thus probing nopredetermined directionality in the EET network, other than that dictated by the potential. While presentinggold nucleation as an alternative to overcome limitations in current production, these results corroboratemain concepts of the relay network model, pushing towards more efficient applications for bio-hybridnanostructured materials in the field of bioelectronics.