In vitro single-cell dissection revealing the interior structure of cable bacteria

Abstract

Filamentous Desulfobulbaceae bacteria were recently discovered as long-range transporters of electrons from sulfide to oxygen in marine sediments. The long-range electron transfer through these cable bacteria has created considerable interests, but it has also raised many questions, such as what structural basis will be required to enable micrometer-sized cells to build into centimeter-long continuous filaments? Here we dissected cable bacteria cells in vitro by atomic force microscopy and further explored the interior, which is normally hidden behind the outer membrane. Using nanoscale topographical and mechanical maps, different types of bacterial cell-cell junctions and strings along the cable length were identified. More important, these strings were found to be continuous along the bacterial cells passing through the cell-cell junctions. This indicates that the strings serve an important function in maintaining integrity of individual cable bacteria cells as a united filament. Furthermore, ridges in the outer membrane are found to envelop the individual strings at cell-cell junctions, and they are proposed to strengthen the junctions. Finally, we propose a model for the division and growth of the cable bacteria, which illustrate the possible structural requirements for the formation of centimeter-length filaments in the recently discovered cable bacteria.

On the evolution and physiology of cable bacteria

“…In contrast, cable bacteria PilA lack the random hook structure for metal interactions, including the exposed tyrosine (Y57), which is predicted to transfer electrons to solid electron acceptors (53,54). Because of this predicted lack of metal interaction capability, the absence of external pili on the outside of cable bacteria filaments (1,9,19,20), and the apparent lack of outer membrane cytochromes (SI Appendix, Table S5) to transfer electrons onto extracellular pili (55), we find it conceivable that PilA in cable bacteria does not form external e-pili but may assemble to internalized, periplasmic fibers.…”

“…A consistent model for cable bacteria metabolism and intra-and intercellular electron transport is currently lacking, and the evolutionary origin of this unique lifestyle remains unclear. Likewise, neither the mechanism of LDET nor the underlying biological structures have been identified; the best candidates are continuous periplasmic fibers of unknown composition that run along the entire filament length and show charge storage capacity (1,19,20).…”

Bacterial synthesis of nanoparticles: A green approach

“…NPs synthesized by bacteria without high-temperature treatment or additional of chemicals have many unique properties. Due to their biocompatibility and stability, they are a real alternative to the physical and chemical methods traditionally used in catalysis (Jiang et al, 2018;Patanjali et al, 2019).…”

Response to referee 1

“…Iron (oxyhydr)oxides are widespread and form in any environment where Fe 2+ -bearing waters come into contact with O 2 (Konhauser and Riding, 2012). In electrogenic sediments, the formation of an iron oxide crust has been observed in both laboratory experiments Rao et al, 2016) and in situ (Seitaj et al, 2015;Sulu-Gambari et al, 2016).…”