Worm tubes as conduits for the electrogenic microbial grid in marine sediments

Area of Science:

• Marine microbiology
• Biogeochemistry
• Sedimentary geology

Background:

• Electrogenic cable bacteria conduct electrons through multicellular filaments, linking redox zones in marine sediments.
• They are typically absent from disturbed or bioturbated sediments.

Purpose of the Study:

• To investigate the presence and ecological role of cable bacteria in bioturbated marine sediments.
• To understand how cable bacteria interact with the tubes of the parchment worm, *Chaetopterus variopedatus*.

Main Methods:

• Field observations of sediment cores from bioturbated areas.
• Microscopic analysis of cable bacteria within parchment worm tubes.
• Geochemical analysis of sediment surrounding the tubes.

Main Results:

• Subsurface cable bacteria aggregations were found associated with *C. variopedatus* tubes in intensely bioturbated sediments.
• Cable bacteria utilize tubes as oxygenated conduits, forming a 3D electron-conducting network into sulfidic zones.
• Their activity elevates pH, promotes metal oxide precipitation, and depletes sulfur around tubes, aiding tube preservation.

Conclusions:

• Cable bacteria are ubiquitous facultative opportunists, not restricted to stable environments.
• Long filaments represent an adaptation to stable redox domains, while shorter filaments indicate broader opportunistic behavior.
• The association with *C. variopedatus* tubes creates a novel microhabitat supporting extensive cable bacterial communities and influencing sediment biogeochemistry.