Enhanced laterally resolved ToF-SIMS and AFM imaging of the electrically conductive structures in cable bacteria

Thiruvallur Eachambadi, R.; Boschker, H. T. S.; Franquet, A.; Spampinato, V.; Hidalgo-Martinez, S.; Valcke, R.; Meysman, F. J. R.; Manca, J. V.

doi:10.1101/2021.01.27.428206

bioRxiv · 10.1101/2021.01.27.428206

Enhanced laterally resolved ToF-SIMS and AFM imaging of the electrically conductive structures in cable bacteria

Thiruvallur Eachambadi, R.·Boschker, H. T. S.·Franquet, A.·Spampinato, V.·Hidalgo-Martinez, S.·Valcke, R.·Meysman, F. J. R.·Manca, J. V.

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Abstract

Cable bacteria are electroactive bacteria that form a long, linear chain of ridged cylindrical cells. These filamentous bacteria perform centimeter-scale long-range electron transport through parallel, interconnected conductive pathways of which the detailed chemical and electrical properties are still unclear. Here, we combine ToF-SIMS (time of flight secondary ion mass spectrometry) and AFM (atomic force microscopy) to investigate the structure and composition of this naturally-occurring electrical network. The enhanced lateral resolution achieved allows differentiation between the cell body and the cell-cell junctions that contain a conspicuous cartwheel structure. Three ToF-SIMS modes were compared in the study of so-called fiber sheaths (i.e., the cell material that remains after removal of cytoplasm and membranes and which embeds the electrical network). Among these, fast imaging delayed extraction (FI-DE) was found to balance lateral and mass resolution, thus yielding multiple benefits in the study of structure-composition relations in cable bacteria: (i) it enables the separate study of the cell body and cell-cell junctions, (ii) by combining FI-DE with in-situ AFM, the depth of Ni-containing protein - key in the electrical transport - is determined with greater precision, and (iii) this combination prevents contamination, which is possible when using an ex-situ AFM. Our results imply that the interconnects in extracted fiber sheaths are either damaged during extraction, or that their composition is different from fibers, or both. From a more general analytical perspective, the proposed methodology of ToF-SIMS in FI-DE-mode combined with in-situ AFM holds great promise for studying the chemical structure of other biological systems.

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Thiruvallur Eachambadi, R., Boschker, H. T. S., Franquet, A., Spampinato, V., Hidalgo-Martinez, S., Valcke, R., Meysman, F. J. R., Manca, J. V.. 2021-01-27. Enhanced laterally resolved ToF-SIMS and AFM imaging of the electrically conductive structures in cable bacteria. https://doi.org/10.1101/2021.01.27.428206

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