Rice is a symbol of life and a representation of prosperity in South Korea. However, studies on the diversity of the bacterial communities in the rhizosphere of rice plants are limited. In this study, four bundles of root samples were collected from the same rice field located in Goyang, South Korea. These were systematically analyzed to discover the diversity of culturable bacterial communities through culture-dependent methods. A total of 504 culturable bacteria were isolated and evaluated for their plant growth-promoting abilities in vitro. Among them, Arthrobacter sp. GN70 was selected for inoculation into the rice plants under laboratory and greenhouse conditions. The results showed a significantly positive effect on shoot length, root length, fresh plant weight, and dry plant weight. Moreover, scanning electron microscopic (SEM) images demonstrated the accumulation of bacterial biofilm networks at the junction of the primary roots, confirming the root-colonizing ability of the bacterium. The strain also exhibited a broad spectrum of in vitro antimicrobial activities against bacteria and fungi. Here, we first report the rice plant growth-promoting ability of the Arthrobacter species with the biofilm-producing and antimicrobial activities against plant and human pathogens. Genome analyses revealed features attributable to enhance rice plant growth, including the genes involved in the synthesis of plant hormones, biofilm production, and secondary metabolites. This study revealed that the rhizobacteria isolated from the roots of rice plants have dual potential to be utilized as a plant growth promoter and antimicrobial agent.

A yellow pigmented, Gram-stain-negative, strictly aerobic, rod-shaped, motile by means of gliding, catalase and oxidase positive bacterium, designated strain DS2-A^T, was isolated from soil. Growth was observed at 4–32°C (optimum, 28°C), pH 6–9 (optimum, 7.0), and with 0–0.25% (w/v) NaCl (optimum, 0%). Phylogenetic analysis of 16S rRNA gene sequence revealed that strain DS2-A^T belonged to the genus Flavobacterium and was most closely related to Flavobacterium aquatile LMG 4008^T (96.4%), Flavobacterium terrae DSM 18829^T (95.6%), Flavobacterium vireti THG-SM1^T (95.5%), Flavobacterium inkyongense IMCC27201^T (95.4%), Flavobacterium brevivitae TTM-43^T (95.2%), and Flavobacterium cucumis DSM 18830^T (95.2%). Strain DS2-A^T produces flexirubin-type pigments. The major fatty acids were iso-C_15:0, iso-C_17:0 3-OH, and iso-C_15:0 3-OH. The major respiratory quinone was identified as menaquinone-6. The major polar lipid was found to be phosphatidylethanolamine. The average nucleotide identity values between strain DS2-A^T and selected taxa, F. aquatile LMG 4008^T, F. terrae DSM 18829^T, and F. cucumis DSM 18830^T, were 72, 72.7, and 71.6%, respectively. The draft genome of strain DS2-A^T has a number of 14 contigs, scaffold N50 of 476,310 bp and a total size of 3,563,867 bp. Additionally, strain DS2-A^T contains 3,127 of gene, 41 of tRNA, 6 of rRNA, and 3 of ncRNA. The DNA G + C content of stain DS2-A^T was 40.7 mol%. Based on phylogenetic and phenotypic analyses, strain DS2-A^T is considered as a novel species of the genus Flavobacterium, for which the name Flavobacterium humi sp. nov., (type strain DS2-A^T = KACC 19715^T = JCM 32786^T) has been proposed.

Two novel bacterial species were isolated from the rhizosphere of Solanum lycopersicum (tomato plant), both exhibiting plant growth-promoting properties. Two isolated strains, Rhodanobacter lycopersici sp. nov. Si-c^T and Rhodanobacter geophilus sp. nov. S2-g^T, were classified through a polyphasic approach, confirming their novel status within the Rhodanobacter genus. The strains demonstrated a remarkable tolerance to extreme pH conditions, with R. lycopersici Si-c^T surviving in pH 3.0–13.0 and R. geophilus S2-g^T tolerating pH 2.0–13.0. Additionally, both strains exhibited multiple plant growth-promoting traits, including indole-3-acetic acid and ammonia production, phosphate solubilization, and siderophore formation. These characteristics suggest that the two strains may play an important role in promoting plant growth, especially in soils with variable pH levels. However, since the direct impact on plant growth was not experimentally tested, the potential of these bacteria for agricultural applications remains to be confirmed through further research. This study expands our understanding of the diversity within the Rhodanobacter genus and provides insights into the potential use of these novel species in sustainable agriculture.

Two bacterial strains, designated MJB4^T and SJ7^T, were isolated from water samples collected from Jeongbang Falls on Jeju Island, Republic of Korea. Phylogenetic analysis of 16S rRNA gene sequences indicated that the two strains belonged to the genera Nocardioides and Hyunsoonleella , owing to their high similarities to Nocardioides jensenii DSM 29641^T (97.5 %) and Hyunsoonleella rubra FA042 ^T (96.3 %), respectively. These values are much lower than the gold standard for bacterial species (98.7 %). The average nucleotide identity values between strains MJB4^T, SJ7^T and the reference strains, Nocardioides jensenii DSM 29641^T, Nocardioides daejeonensis MJ31^T and Hyunsoonleella flava T58^T were 77.2, 75.9 and 75.4 %, respectively. Strains MJB4^T and SJ7^T and the type strains of the species involved in system incidence have average nucleotide identity and average amino acid threshold values of 60.1–82.6 % for the species boundary (95–96 %), which confirms that strains MJB4^T and SJ7^T represent two new species of genus Nocardioides and Hyunsoonleella , respectively. Based on phylogenetic and phenotypic data, strains MJB4^T and SJ7^T are considered to represent novel species of the genus Nocardioides and Hyunsoonleella , respectively, for which the names Nocardioides donggukensis sp. nov. (type strain MJB4^T=KACC 21724^T=NBRC 114402^T) and Hyunsoonleella aquatilis sp. nov., (type strain SJ7^T=KACC 21715^T=NBRC 114486^T) have been proposed.

In this study, four novel bacterial strains, USB13^T, AW1^T, GTP1^T, and HM2^T, were isolated from various environments in Busan and Jeju Island, Republic of Korea. The 16S rRNA sequencing results indicated that the four novel strains belong to the genusRamlibacter.All four strains were tested for their potential cellulolytic properties, where strain USB13^Twas identified as the only novel bacterium and the first within its genus to show cellulolytic activity. When tested, the highest activities of endoglucanase, exoglucanase,β-glucosidase, and filter paper cellulase (FPCase) were 1.91 IU/mL, 1.77 IU/mL, 0.76 IU/mL, and 1.12 IU/mL, respectively at pH 6.0. Comparisons of draft whole genome sequences (WGS) were also made using average nucleotide identity, digital DNA-DNA hybridization values, and average amino acid identity values, while whole genome comparison was visualized using the BLAST Ring Image Generator. The G + C contents of the strains ranged from 67.9 to 69.9%, while genome sizes ranged from 4.31 to 6.15 Mbp. Based on polyphasic evidence, the novel strains represent four new species within the genusRamlibacter, for which the namesRamlibacter cellulosilyticussp. nov. (type strain, USB13^T = KACC 21656^T = NBRC 114839^T)Ramlibacter aurantiacussp. nov. (type strain, AW1^T = KACC 21544^T = NBRC 114862^T),Ramlibacter albussp. nov. (type strain, GTP1^T = KACC 21702^T = NBRC 114488^T), andRamlibacter pallidussp. nov. (type strain, HM2^T = KCTC 82557^T = NBRC 114489^T) are proposed.