Filamentous electroactive microorganisms promote mass transfer and sulfate reduction in sediment microbial electrochemical systems

Electron transfer and mass transfer are critical processes for efficient sediment remediation using sediment microbial electrochemical systems (SMESs). Increasing reports show that filamentous electroactive microorganisms (f-EAMs) that widely exist in heterogeneous sediments play essential roles in biogeochemical cycles and sediment remediation, significantly impacting process efficiencies. However, the knowledge of the mechanism of f-EAMs in biogeochemical cycles and sediment remediation is still limited. This study investigated the spatiotemporal effect of a unicellular Gram-positive f-EAM, Lysinibacillus varians GY32, on the sulfur cycle in SMESs. The results showed that adding L. varians GY32 into sediments could significantly decrease the diffusion resistances of the sediments by up to 49.4% and reduce the porewater sulfate concentrations by up to 46.4%, which validated that L. varians GY32 contributed to enhancing the mass transfer and sulfate reduction in sediments. Meanwhile, the vertical difference in diffusion resistances and porewater sulfate concentrations was reduced. The dynamics of electrochemical and physicochemical properties of sediments coincided well with the enrichment of filamentous microorganisms, sulfate-reducing bacteria, EAMs (especially f-EAMs), and syntrophic bacteria, as well as the reinforcement of the community interactions that took the above microorganisms as core members. Our findings provide novel insights for understanding the underlying mechanism of f-EAMs in biogeochemical cycles and sediment remediation.