Morphological Study of Cell Envelope in Electron Conducting Cable Bacteria

Abstract

Recently, filamentous and unbranched cable bacteria were discovered in marine sediments where they couple sulfide oxidation to oxygen reduction over centimeter-scale distances[1]. Remarkably, cells cooperate to conduct electrons, providing energy along the whole filament, overthrowing the long-held conviction that each cell provides its own energy[2][3]. Identifying the conductive structure and the mechanism of this long-distance electron transfer will not only expand our knowledge on the role of cable bacteria in marine environments but also further extend the areas of applications in bioelectronics and bioremediation. In this work, we examined the architecture of the cell envelope by investigating intact filaments and filaments that were treated to remove the cytoplasm and membranes, using various physical characterization techniques with a particular emphasis on Scanning Probe Microscopy techniques. The illustrative AFM image in figure 1 [d] shows a fiber cage structure residing in the periplasmic space, attributed to the conducting units occurring universally in different species of cable bacteria. Based on our findings, we thereby propose that the Desulfobulbaceae family is composed of a common type of conductive fibers, which defines the diameter of the cable bacteria by its quantity.