In this paper, two classical organic electron donors, i.e. acetate and glucose, were chosen to study the oxidation of organics coupling with denitratation enrichment culture via batch tests and to predicate its key functional bacteria via genomes-based metagenomics. The results showed that acetate-denitratation was observed to have better denitratation performances (nitrate reduction rate of 13.5-18.5 mg.g(-1)VSS.h(-1) and nitrite yield of 96.2%) than glucose-denitratation (nitrate reduction rate of 4.6-6.5 mg.g(-1)VSS.h(-1) and nitrite yield of 71.5%). Distinctive but preferable acetogenesis (acetate production) step was observed in glucose-fed test, which resulted in the decline of denitratation performance by lower intracellular NADH/NAD(+) ratio. The enzymatic assay of key carbon metabolism indicated that the low NADH/NAD(+) ratio was likely impacted by up-regulating the acetate generation from glucose and down-regulating the acetate utilization. Metagenomic binning and phylogenetic analysis revealed that a new Halomonas genome (only shared an average nucleotide identify of 83% to the most related species) dominated in the system, and was most likely responsible for this kind of acetogenesis in denitratation. The findings of this work are important for both the development of denitratation-based nitrogen removal technology and the insight into fundamental microbial metabolism of nitrogen coupling carbon oxidation.