Characterization and comparative genomic analysis of <i>Pseudaeromonas aegiceratis</i> sp. nov., a new nitrogen-fixing bacterium from the sediments of mangrove plant <i>Aegiceras corniculatum</i>

A gram-negative, nitrogen-fixing, rod-shaped, and motile bacterium, designated as ZJS20^T, was isolated from the sediments of <i>Aegiceras corniculatum</i> in Zhanjiang, Guangdong, China. The growth of strain ZJS20^T occurred at 10°C-45°C, pH 5.5-8.0, and in 0%-3% (wt/vol) NaCl. Strain ZJS20^T had the highest sequence similarity of 16S rRNA gene with <i>Pseudaeromonas paramecia</i> PCS8^T (98.5%), followed by <i>Pseudaeromonas sharmana</i> GPTSA-6^T (97.1%) and <i>Pseudaeromonas pectinilytica</i> AR1^T (96.7%). The phylogenetic trees built using 16S rRNA genes and Type (Strain) Genome Server both revealed that strain ZJS20^T fell into a cluster with <i>Pseudaeromonas</i> sp. strains. The genome of strain ZJS20^T has a 3,681,671 bp circular chromosome, a G + C content of 62.7%, and 3,320 proteins-coding genes. The genome contains <i>nif</i> and <i>anf</i> genes for the synthesis of Mo- and Fe-nitrogenase and genes related to plant growth-promoting traits. Both the digital DNA-DNA hybridization and average nucleotide identity values between strain ZJS20^T and type strains of the genus <i>Pseudaeromonas</i> were below the cutoff thresholds for species demarcation. The profiles of the predominant fatty acids, major polar lipids, and respiratory quinone of strain ZJS20^T were similar to those of other <i>Pseudaeromonas</i> species. According to the above results, strain ZJS20^T is considered to be a novel species of the genus <i>Pseudaeromonas</i>, with the proposed name <i>Pseudaeromonas aegiceratis</i> sp. nov. The type strain is ZJS20^T (MCCC 1K08760^T = KCTC 8214^T). This study expands the membership of the genus <i>Pseudaeromonas</i> and reveals the potential of this genus to be used as plant growth-promoting bacteria with their outstanding nitrogen-fixation ability.IMPORTANCE<i>Pseudaeromonas</i> is a genus known as close to the genus <i>Aeromonas</i> and contains only three species, which were isolated from different sources. Except for the physio-biochemical properties, other characteristics, such as genomic information and functions of the genus, have been reported scarcely to date. Here, the study reports the fourth species (<i>Pseudaeromonas aegiceratis</i> ZJS20^T) to the genus <i>Pseudaeromonas</i> and reveals its nitrogen-fixation capacity. Comparative genomic analyses revealed that genomes of strain ZJS20^T and other type <i>Pseudaeromonas</i> strains all contain <i>nif</i> genes (<i>nifBHDKENXV</i>) for the synthesis of Mo-nitrogenase, as well as genes related to phosphate metabolism and auxin synthesis. Therefore, we proposed that <i>Pseudaeromonas</i> sp. could be considered as a new and potential plant growth-promoting bacteria to be used in agriculture, although in-depth experiments are needed in the future to verify their specific plant growth-promoting traits.