Cable Bacteria Accelerate Nitrogen Removal in Freshwater Sediments by Mitigating Diffusion Limitation via...

The sustainable remediation of nitrogen polluted aquatic sediments is often constrained by the spatial separation of electron donors and acceptors, which limits intrinsic microbial nitrogen removal. The long-distance electron transport capacity of cable bacteria offers a natural strategy to overcome this limitation but the kinetic mechanisms remains poorly understood. Herein cable bacteria were enriched from ammonia impacted freshwater sediments and their role in enhancing nitrogen removal was systematically investigated. Biogeochemical analysis showed that cable bacteria reduced ammonium by 93% and increased sulfate accumulation 2.07 times relative to controls. Critically, DGT induced fluxes in sediments and soils (DIFS) modeling at depths of 4 mm and 20 mm revealed that cable bacteria maintained uniformly low nitrate and ammonium diffusion fluxes, whereas in the control nitrate fluxes were 4.5-fold higher and ammonium fluxes were 8.9- to 53-fold higher. This kinetic evidence indicates that cable bacteria accelerate nitrogen removal by enhancing the coupling between nitrification and denitrification, thereby mitigating the classical diffusion limitation that restricts these processes in surface sediments. Metagenomic analysis showed that cable bacteria orchestrated a community shift increasing Nitrospira abundance from 0.4% to 20% and enriching genes for respiratory nitrate reduction (narG) and assimilatory sulfate reduction (cysH, sir), establishing a self-sustaining syntrophic network that coordinated nitrogen and sulfur fluxes. These findings establish cable bacteria as a promising bioremediation tool for cleaner nitrogen management in contaminated aquatic systems.