Duganella hordei sp. nov., Duganella caerulea sp. nov., and Duganella rhizosphaerae sp. nov., isolated from barley rhizosphere

Duganella sp. strains R1T, R57T, and R64T, isolated from barley roots in Japan, are Gram-stain-negative, motile, rod-shaped bacteria. Duganella species abundantly colonized barley roots. Strains R1T, R57T, and R64T were capable of growth at 4 °C, suggesting adaptation to colonize winter barley roots. Strains R57T and R64T formed purple colonies, indicating violacein production, while strain R1T did not. Based on 16S rRNA gene sequence similarities, strains R1T, R57T, and R64T were most closely related to D. violaceipulchra HSC-15S17T (99.10%), D. vulcania FT81WT (99.45%), and D. violaceipulchra HSC-15S17T (99.86%), respectively. Their genome sizes ranged from 7.05 to 7.38 Mbp, and their genomic G+C contents were 64.2–64.7%. The average nucleotide identity and digital DNA–DNA hybridization values between R1T and D. violaceipulchra HSC-15S17T, R57T and D. vulcania FT81WT, R64T and D. violaceipulchra HSC-15S17T were 86.0% and 33.2%, 95.7% and 67.9%, and 92.7% and 52.6%, respectively. Their fatty acids were predominantly composed of C16:0, C17:0 cyclo, and summed feature 3 (C16:1 ω7c and/or C16:1 ω6c). Based on their distinct genetic and phenotypic characteristics, and supported by chemotaxonomic analyses, we propose that strains R1T, R57T, and R64T represent novel species within the Duganella genus, for which the names Duganella hordei (type strain R1T = NBRC 115982 T = DSM 115069 T), Duganella caerulea (type strain R57T = NBRC 115983 T = DSM 115070 T), and Duganella rhizosphaerae (type strain R64T = NBRC 115984 T = DSM 115071 T) are proposed.