Enhancing water toxicity determination sensitivity by using TMAO as electron acceptor of inward extracellular electron transfer in electrochemically active bacteria

Toxicity determination based on electrochemically active bacteria (EAB) shows great prospects for early warning of sudden water pollution. However, the main bottleneck for practical application is the low sensitivity. Extracellular electron transfer (EET) is a key parameter influencing sensitivity. Our previous research has demonstrated that EAB exhibit higher sensitivity when performing inward EET compared with outward EET. Inward EET relies on electron acceptors, but the effects of electron acceptors on sensitivity remain unclear. In this study, the sensitivity of toxicity determination with different electron acceptors was compared. Results indicated that the choice of electron acceptors significantly changed the sensitivity. When Trimethylamine N-oxide (TMAO) was chosen as the electron acceptor, EAB exhibited the highest sensitivity, with a lower response limit of 0.05 mg/L Cd²⁺. The main reason was that the utilization of TMAO for inward EET increases the membrane permeability of EAB cells, facilitates toxic pollutant penetration, and results in high mortality after toxicity exposure.