Aerobic extracellular electron transfer in Shewanella spp

Microbial extracellular electron transfer (EET) can convert chemical energy directly into electron flow and is pivotal in wastewater treatment, power generation and biogeochemical cycles. However, it is widely believed that this process can only occur under anaerobic or micro-aerobic conditions, which poses severe limitations to applications of microbial EET processes. Here, we report that an EET model strain, Shewanella oneidensis MR-1 can activate counterintuitive EET processes to output electron flow also under high dissolved oxygen conditions, i.e. aerobic EET. Significantly, bio-electrochemical system under high dissolved oxygen conditions was found to give a 5-fold higher current density compared to commonly known anaerobic conditions. The underlying mechanism suggests that although high dissolved oxygen (>4.0 mg/L) reduces the effectiveness of electron shuttles, it supports a greater biological capacity and faster metabolic processes. We have also found that aerobic EET process can reduce effectively the manganese mineral birnessite aerobically, offering insights into the biogeochemical cycling of manganese. Furthermore, this aerobic EET processes were also identified in several Shewanella species.