Different mechanisms for riboflavin to improve the outward and inward extracellular electron transfer of Shewanella loihica

Exploring extracellular electron transfer (EET) is important to promote the applications of electrochemically active bacteria (EAB). Shewanella loihica PV-4, which is a model EAB capable of bidirectional EET, has shown promising application prospects in water quality monitoring and nitrogen removal. However, its bidirectional EET mechanism is not clear yet. This study focused on the electrochemical characteristics and electron transfer processes of S. loihica PV-4 bidirectional EET. Results revealed that riboflavin (RF) facilitates both the outward and inward EET, and the enhancement mechanism depends on EET direction. When S. loihica PV-4 performs outward EET, free RF acts as a redox mediator to promote electricity production. When the EET direction is reversed, bound RF is involved in electricity consumption. These results elucidated the effect of RF on S. loihica PV-4 bidirectional EET, providing a basis for the enhancement of S. loihica PV-4 EET.