A mathematical model for electrochemically active filamentous sulfide-oxidising bacteria

Area of Science:

• Geomicrobiology
• Biogeochemistry
• Mathematical modeling

Background:

• Ocean sediments host filamentous bacteria capable of long-distance electron transfer.
• These microbes play a crucial role in biogeochemical cycling of sulfur and oxygen.
• Understanding their spatial distribution and metabolic activity is key to marine ecosystem studies.

Purpose of the Study:

• To develop a mathematical model for filamentous sulfur-oxidizing bacteria.
• To analyze the mechanisms of electron conduction and ion transport along bacterial filaments.
• To predict biomass growth patterns and substrate consumption in marine sediments.

Main Methods:

• Developed a mathematical model incorporating Nernst-Planck diffusion, ion migration, and Ohm's law.
• Simulated electron conduction between reactive zones within filamentous bacteria.
• Analyzed metabolic activity and biomass growth dynamics.

Main Results:

• Simulations predict outward biomass growth, forming anode (sulfide consumption) and cathode (oxygen consumption) zones.
• Initial inward fluxes of 4.6 mmol O2/m(2)/d and 2.5 mmol S/m(2)/d were observed.
• Final fluxes reached 8.2 mmol O2/m(2)/d and 4.34 mmol S/m(2)/d, increasing with growth.
• Controlling mechanisms shifted from biomass to substrate or conductivity limitation with increasing filament length.

Conclusions:

• The model successfully replicates observed biological consumption of oxygen and sulfide in sediments.
• Electron conduction is crucial for facilitating redox reactions over long distances.
• Discrepancies in growth rates suggest potential alternative metabolisms or use of secondary substrates by these microbes.