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[Display omitted] • Strain MFG10 exhibits excellent denitrification and manganese reduction abilities. • MnO 2 promoted the metabolism and induced extracellular secretion by MFG10. • SMP composition changed to improve degradability and redox activity. • The EET process was enhanced by the trapping-solubilizing MnO 2 mechanism of EPS. • Tryptophan-like proteins and PS become potential electron donor precursors. In this study, the manganese (Mn) reduction-coupled denitrification strategy of dissimilatory Mn reducing bacteria was insightfully investigated. Different parameters (MnO 2 level, pH, and temperature) were optimized by kinetic fitting to improve denitrification and Mn reduction effects. The 300 mg L−1 MnO 2 addition achieved 98.72% NO 3 –-N removal in 12 h, which was 54.62% higher than blank group without MnO 2. Scale-up studies showed that the metabolic activity of the bacteria was effectively enhanced by the addition of MnO 2. Besides the deepening of humification in the system, tryptophan-like protein and polysaccharide as potential electron donor precursors revealed remarkable contributions to the extracellular secretion-dependent denitrification process of DMRB. The effect of EPS on Mn reduction depends mainly on the capture of MnO 2 by the LB-EPS layer versus its dissolution in the TB-EPS layer. Ultimately, the EPS possess a dual effect of accelerated denitrification and Mn reduction efficiency due to the enhanced EET process. [ABSTRACT FROM AUTHOR]