The role of anthraquinone-2-sulfonate on intra/extracellular electron transfer of anaerobic nitrate reduction

To improve the electron (e(-) ) transfer efficiency, exogenous redox mediators (RMs) were usually employed to enhance the denitrification efficiency due to the electron shuttling. Previous studies were mainly focused on how to improve the extracellular electron transfer (EET) by exogenous RMs. However, the intracellular electron transfer (IET), another crucial e(-) transfer pathway, of biological denitrification was scarcely reported, especially for the relationship between the denitrification and IET. In this study, Coenzyme Q, Complexes I, II and III were determined as the core components in the IET chain of denitrification by using four specific respiration chain inhibitors (RCIs). Anthraquinone-2-sulfonate (AQS) partially recovered the IET of denitrification from NO3 -N to N2 gas when the RCIs were added. Specifically, the generations of N2 gas were improved by 9.68%-18.25% in the experiments with RCIs and AQS, comparing to that with RCIs. nrfA gene was not detected by reverse transcription-polymerase chain reaction, suggesting that Klebsiella oxytoca strain could not conduct dissimilatory nitrate reduction to ammonium. Nitrate assimilation was considered as the main NH4+-N formation way of K. oxytoca strain. The two exe213; transfer pathways of denitrification were constructed and the roles of AQS on the IET and EET of denitrification were specifically discussed. The results of this study provided a better understanding of the ee213; transfer pathways of denitrification, and suggested a potential practical use of exogenous RM on bio-treatment of nitrate-containing wastewater.

Automated summary

To enhance the denitrification efficiency, exogenous redox mediators (RMs) are commonly used to improve electron transfer. Previous studies have focused on improving extracellular electron transfer (EET) through the use of RMs, but the intracellular electron transfer (IET) of biological denitrification has been rarely reported. This study identified the core components in the IET chain of denitrification and investigated the role of a specific redox mediator in enhancing IET. The results provide a better understanding of the electron transfer pathways of denitrification and suggest a potential practical application for exogenous RMs in nitrate-containing wastewater treatment.