Nitrate reduction serves as a pivotal process in the global nitrogen cycle, playing a crucial role in natural ecosystems and industrial applications. Although the genus is not traditionally regarded as a nitrate reducer, several strains have recently been found to be capable of doing so. However, the evolutionary trajectory of this capability remains undiscovered. In this study, 32 bacterial strains were isolated and cultivated from the tidal flat sediment in Hangzhou Bay and classified into the classes (n = 2), (n = 2), (n = 17), (n = 5), and (n = 6). One nitrate-reducing strain, designated as CYL-A6, was identified by polyphasic taxonomy and proposed as a novel species. Genomic analysis reveals that seven genomes encode the dissimilatory nitrate reduction genes . Evolutionary analysis showed that these three nitrate-reducing genes were present in the early common ancestor of the genus , while gene loss events occurred in the subsequent evolution. With the loss of nitrate-reducing genes in the ancestry nodes, a wide variety of genes related to energy production and conversion, as well as carbohydrate, nucleotide, coenzyme, and inorganic ion metabolism, were gained in those nodes, which enabled members to utilize diverse substrates for increased energy production. This study enhances the understanding of microbial diversity in marine tidal flat sediments, proposes a novel nitrate-reducing species of the genus , and highlights the ecological diversification and ecological niche breadth in the evolution of the microbial metabolic network.