Acetate is an abundant carbon source that can trigger microbial redox processes in anoxic environments, thereby affecting the microbial community structure, function, and associated element cycling. Here, we investigated the acetate-assimilating microbial community, especially the key microorganisms involved in nitrate-dependent Fe (II) oxidation that are closely associated with soil redox processes in flooded soil. In the present study, DNA-stable isotope probing (DNA-SIP) with labeled acetate (C-13) as a carbon source was applied to examine the acetate-assimilating communities associated with nitrate-dependent Fe(II) oxidation. The results showed that NO3- was rapidly reduced in the treatments with NO3- and NO3- + Fe(II). Fe(II) oxidation occurred quickly only in the presence of NO3-. In the treatments with acetate only, the predominant C-13-labeled genera such as Geobacter, Azospira, Azospirillum, Ideonella, and Desulfovibrionia were probably involved in acetate oxidation coupled with the redox processes of NO3-, Fe(III) and SO42- reduction, which are the most important electron acceptors in flooded soils. The addition of NO3- and Fe(II) significantly affected the acetate-assimilating microbial community from the original soil. The enriched genera in C-13 heavy fractions were associated with Pseudogulbenkiania, Azospira, Zoogloea, Azoarcus, and Bdellovibrio dominated in the treatments with NO3- and Fe(II). In the treatments with NO3- only, Zoogloea, Azospira, Azoarcus, and Geothrix were the dominant genera. Given the different genera with enrichments in C-13-heavy fractions in different treatments, Zoogloea and Pseudogulbenkiania were identified as key microorganisms associated with NO3- reduction and nitrate-dependent Fe(II) oxidation, respectively. These findings suggest the importance of Zoogloea and Pseudogulbenkiania for C, Fe, and N biogeochemistry and indicate that Fe and N cycling have a great impact on soil biogeochemistry processes.

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