title: The effects of fulvic acid on microbial denitrification: promotion of NADH generation, electron transfer, and consumption.
abstract: The heterotrophic denitrification requires the participation of electrons which are derived from direct electron donor (usually nicotinamide adenine dinucleotide (NADH)), and the electrons are transferred via electron transport system in denitrifiers and then consumed by denitrifying enzymes. Despite the reported electron transfer ability of humic substances (HS), the influences of fulvic acid (FA), an ubiquitous major component of HS, on promoting NADH generation, electron transfer, and consumption in denitrification process have never been reported. The presence of FA, compared with the control, was found not only significantly improved the total nitrogen (TN) removal efficiency (99.9 % versus 74.8 %) but remarkably reduced the nitrite accumulation (0.2 against 43.8 mg/L) and N2O emission (0.003 against 0.240 mg nitrogen/mg TN removed). The mechanisms study showed that FA increased the metabolism of carbon source via glycolysis and tricarboxylic acid (TCA) cycle pathways to produce more available NADH. FA also facilitated the electron transfer activities from NADH to denitrifying enzymes via complex I and complex III in electron transport system, which improved the reduction of nitrate and accelerated the transformations of nitrite and N2O, and lower nitrite and N2O accumulations were therefore observed. In addition, the consumption of electrons in denitrification was enhanced due to FA stimulating the synthesis and the catalytic activity of key denitrifying enzymes, especially nitrite reductase and N2O reductase. It will provide an important new insight into the potential effect of FA on microbial denitrification metabolism process and even nitrogen cycle in nature niches.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China.
authors.forename: Mu
authors.initials: M
authors.lastname: Li
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China.
authors.forename: Yinglong
authors.initials: Y
authors.lastname: Su
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China. yg2chen@yahoo.com.
authors.forename: Yinguang
authors.initials: Y
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Wan
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China.
authors.forename: Xiong
authors.initials: X
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China.
authors.forename: Kun
authors.initials: K
authors.lastname: Liu
mesh_terms: D001578:Benzopyrans / Q000494:pharmacology*; D019149:Bioreactors; D002244:Carbon / Q000378:metabolism; D058440:Denitrification / Q000187:drug effects*; D004579:Electron Transport; D052836:Heterotrophic Processes; D009243:NAD / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010231:Paracoccus denitrificans / Q000187:drug effects* / Q000378:metabolism*; D014865:Waste Disposal, Fluid
chemical_list: D001578:Benzopyrans; D009566:Nitrates; D009573:Nitrites; D009243:NAD; D002244:Carbon; D009584:Nitrogen; C005023:fulvic acid
keywords: Denitrification; Electrons; Fulvic acid; NADH; Promote