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.

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.

A Gram-stain-negative, aerobic and non-motile bacterium, strain sand1-3^T, was isolated from beach sand collected from Haeundae Beach located in Busan, Republic of Korea. Based on the results of 16S rRNA gene sequence and phylogenetic analyses, Sphingomonas daechungensis CH15-11^T (97.0 %), Sphingomonas edaphi DAC4^T (96.8 %), Sphingomonas xanthus AE3^T (96.5 %) and Sphingomonas oryziterrae YC6722^T (96.0 %) were selected for comparing phenotypic and chemotaxonomic characteristics. Cells of strain sand1-3^T grew at 7–50 °C (optimum, 30–35 °C), pH 5.0–8.0 (optimum, pH 7.0–8.0) and in the presence of 0–0.5 % (w/v) NaCl (optimum, 0 %). Major polar lipids included diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, sphingoglycolipid, one unidentified glycolipid and one unidentified phosphoglycolipid. The major fatty acids were summed feature 8 (C_18 : 1 ω6c and/or C_18 : 1 ω7c) and C_18 : 1 2-OH. Moreover, the sole respiratory quinone and major polyamine were identified as ubiquinone-10 and homospermidine, respectively. The genomic DNA G+C content was 65.9 mol%. The digital DNA–DNA hybridization, average nucleotide identity and average amino acid identity values of strain sand1-3^T and its reference strains with publicly available genomes were 17.9–18.9 %, 72.0–75.3 % and 63.3–76.5 % respectively. Based on polyphasic evidence, we propose Sphingomonas sabuli sp. nov. as a novel species within the genus Sphingomonas . The type strain is sand1-3^T (=KCTC 82358^T=NBRC 114538^T).

A Gram-negative, moderately halophilic bacterium, designated as strain Y3S6^T, was isolated from a surface seawater sample collected from Dongangyoeng cave, Udo-myeon, Jeju-si, Jeju-do, Repulic of Korea. Cells of strain Y3S6^T were aerobic, rod-shaped, non-sporulated, yellow, catalase- negative, oxidase-negative and motile with one polar flagellum. Growth of strain Y3S6^T occurred at 15–40 °C (optimum: 25–30 °C), at pH 6.0–9.0 (optimum: pH 7.0) and in the presence of 0–13% NaCl (optimum: 1–6 %, w/v). The novel strain was able to produce carotenoids. Its chemotaxonomic and morphological characteristics were consistent with those of members of the genus Halomonas . Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain Y3S6^T formed a clade with Halomonas pellis L5^T (98.97 %) and Halomonas saliphila LCB169^T(98.90%). The average nucleotide identity and digital DNA–DNA hybridization values of strain Y3S6^T with the most closely related strains for which whole genomes are publicly available were 82.3–85.2% and 62.8–66.1 %, respectively. The major fatty acids in strain Y3S6^T were C_16 : 0, C_19 : 0 cyclo ω8c and summed feature 8 (composed of C_18 : 1 ω7c and/or C_18 : 1 ω6c), and the predominant quinone was Q-9. Its polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two unidentified phosphoglycolipid, one unidentified phosphoaminoglycolipid and one unidentified phospholipid. The genomic DNA G+C content based on the draft genome sequence was 64.2 mol%. The results of physiological and biochemical tests and 16S rRNA sequence analysis clearly revealed that strain Y3S6^T represents a novel species in the genus Halomonas , for which the name Halomonas antri sp. nov. has been proposed. The type strain is Y3S6^T (=KACC 21536^T=NBRC 114315=TBRC 15164^T).

A novel Gram-stain-negative, aerobic, asporogenous, catalase-positive and oxidase-negative, non-motile, golden-yellow pigmented, rod-shaped bacterium with casein-degrading ability, designated strain GCR10T, was isolated from roots of rice plants collected from a paddy field near Dongguk University, Republic of Korea. The results of subsequent 16S rRNA gene sequence analysis indicated that GCR10T shares the highest sequence identity with Chryseobacterium piscicola VQ-6316sT (98.3%). Strain GCR10T grew at 2–32 °C (optimum, 25 °C), at pH 6.0–8.0 (optimum, pH 7.0) and in the presence of 0–2.0% (w/v) NaCl (optimum in the absence of NaCl). The novel strain was able to produce carotenoid and flexirubin-type pigments. The predominant menaquinone was MK-6 and the major fatty acids were identified as iso-C15 : 0, iso-C17 : 0 3-OH and iso-C17 : 1ω9c. The polar lipids were phosphatidylethanolamine, four unidentified aminoglycolipids, two unidentified aminolipids and two unidentified glycolipids. The genome of GCR10T is 4.3 Mb in length with a DNA G+C content of 36.5 mol%. Average nucleotide identity, digital DNA–DNA hybridization and average amino acid identity values between GCR10T and Chryseobacterium piscicola VQ-6316sT were 82.1, 25.2 and 84.3 %, respectively, which clearly indicates that the novel strain is distinct from its closest relative. The demand for natural biodegradable pigments isolated frominsects, plants or microorganisms is increasing day by day because of their beneficial pharmacological properties. Here, we describe a novel strain that produces two types of pigment, carotenoid and flexirubin. On the basis of the results from phenotypic, genotypic and chemotaxonomic analyses, strain GCR10T represents a novel species of the genus Chryseobacterium , and the name Chryseobacterium caseinilyticum sp. nov. is proposed. The type strain is GCR10T (=KACC 21707T=NBRC 114715T).