| Summary: | Heterotrophic nitrification–aerobic denitrification (HN-AD) is an efficient nitrogen removal process and the genus <i>Paracoccus</i> is one important group of the HN-AD bacteria. During an investigation of the microbial diversity in marine ranching of the Pearl River Estuary (PR China), three bacterial strains, designated SCSIO 75817<sup>T</sup>, SCSIO 76264<sup>T</sup> and SCSIO 80058<sup>T</sup>, were isolated from sediments. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the three strains belonged to the genus <i>Paracoccus</i> and their closest neighbors were <i>P. isoporae</i> DSM 22220<sup>T</sup> (97.6–98.0%), <i>P</i>. <i>aurantiacus</i> CGMCC 1.13898<sup>T</sup> (97.3–97.6%) and <i>P</i>. <i>xiamenensis</i> MCCC 1A16381<sup>T</sup> (97.1–97.4%), respectively. The analysis results of 16S rRNA gene similarity, ANI, AAI and dDDH showed that the pairwise similarities between these three strains and their closest neighbors were 97.4–98.5%, 76.9–81.0%, 75.5–79.6% and 20.3–23.3%, respectively. Polyphasic taxonomic data of the phylogenetic, phenotypic and chemotaxonomic analyses indicate that these strains represent three novel species in the genus <i>Paracoccus</i>, for which the names <i>Paracoccus aerodenitrificans</i> sp. nov., <i>Paracoccus sediminicola</i> sp. nov. and <i>Paracoccus albus</i> sp. nov. are proposed, respectively. The study also demonstrated the heterotrophic nitrification–aerobic denitrification (HN-AD) ability of the novel species <i>P. aerodenitrificans</i> SCSIO 75817<sup>T</sup>. When it was aerobically cultivated at 28 °C using NH<sub>4</sub><sup>+</sup>-N, NO<sub>3</sub><sup>−</sup>-N and NO<sub>2</sub><sup>−</sup>-N as the sole nitrogen sources, the nitrogen removal efficiencies were 73.4, 55.27 and 49.2%, respectively, and the maximum removal rates were 3.05, 1.82 and 1.63 mg/L/h, respectively. The results suggest that it has promising potential for wastewater treatment.
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