Characterization and comparative genomic analysis of sp. nov., a new nitrogen-fixing bacterium from the sediments of mangrove plant .

A gram-negative, nitrogen-fixing, rod-shaped, and motile bacterium, designated as ZJS20, was isolated from the sediments of in Zhanjiang, Guangdong, China. The growth of strain ZJS20 occurred at 10°C-45°C, pH 5.5-8.0, and in 0%-3% (wt/vol) NaCl. Strain ZJS20 had the highest sequence similarity of 16S rRNA gene with PCS8 (98.5%), followed by GPTSA-6 (97.1%) and AR1 (96.7%). The phylogenetic trees built using 16S rRNA genes and Type (Strain) Genome Server both revealed that strain ZJS20 fell into a cluster with sp. strains. The genome of strain ZJS20 has a 3,681,671 bp circular chromosome, a G + C content of 62.7%, and 3,320 proteins-coding genes. The genome contains and 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 and type strains of the genus were below the cutoff thresholds for species demarcation. The profiles of the predominant fatty acids, major polar lipids, and respiratory quinone of strain ZJS20 were similar to those of other species. According to the above results, strain ZJS20 is considered to be a novel species of the genus , with the proposed name sp. nov. The type strain is ZJS20 (MCCC 1K08760 = KCTC 8214). This study expands the membership of the genus and reveals the potential of this genus to be used as plant growth-promoting bacteria with their outstanding nitrogen-fixation ability.IMPORTANCE is a genus known as close to the genus 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 ( ZJS20) to the genus and reveals its nitrogen-fixation capacity. Comparative genomic analyses revealed that genomes of strain ZJS20 and other type strains all contain genes () for the synthesis of Mo-nitrogenase, as well as genes related to phosphate metabolism and auxin synthesis. Therefore, we proposed that 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.