Characterization of the conductive structures in the periplasm of cable bacteria using combined TOF-SIMS/AFM

Abstract

Filamentous cable bacteria were recently discovered in marine sediments and are capable of transporting electrons inside their body over centimeter-scale distances [1]. This length scale of electron transport is more than three orders of magnitude greater than previously known in biology [2]. Identifying the conductive structures and the mechanism of this long-distance electron transfer will not only expand our knowledge of the role of cable bacteria in marine environments, but also could lead to novel applications in bioelectronics and microbial fuel cells.

Recently, it was discovered shown that conductive structures are located in the cell envelope of cable bacteria. In this study, this conductive fiber envelope was extracted from cable bacteria, and TOF-SIMS was used to characterize the extracted material. TOF-SIMS was operated in the dual beam acquisition mode, where the Argon Gas Cluster Ion Beam (GCIB) was used as the sputter beam and Bismuth (Bi3) was used as the analysis beam.

An in-situ AFM in contact mode was used to calibrate sputtering depths and to identify the positions of the layers. TOF-SIMS indicated that the fiber envelope is first made of a layer of protein followed by a carbohydrate layer. Based on the TOF-SIMS results, we will present a model where the conductive fibers are made of protein core, which are held together by a sheet of polysaccharide, most likely in the form of peptidoglycan. Proteomics would be the logical next step to further identify the proteins and sugars and their role in electron conductivity.

TOF-SIMS analysis was financially supported by the HERCULES foundation.