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

Duganella sp. strains R1^T, R57^T, and R64^T, isolated from barley roots in Japan, are Gram-stain-negative, motile, rod-shaped bacteria. Duganella species abundantly colonized barley roots. Strains R1^T, R57^T, and R64^T were capable of growth at 4 °C, suggesting adaptation to colonize winter barley roots. Strains R57^T and R64^T formed purple colonies, indicating violacein production, while strain R1^T did not. Based on 16S rRNA gene sequence similarities, strains R1^T, R57^T, and R64^T were most closely related to D. violaceipulchra HSC-15S17^T (99.10%), D. vulcania FT81W^T (99.45%), and D. violaceipulchra HSC-15S17^T (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 R1^T and D. violaceipulchra HSC-15S17^T, R57^T and D. vulcania FT81W^T, R64^T and D. violaceipulchra HSC-15S17^T 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 R1^T, R57^T, and R64^T represent novel species within the Duganella genus, for which the names Duganella hordei (type strain R1^T = NBRC 115982 ^T = DSM 115069 ^T), Duganella caerulea (type strain R57^T = NBRC 115983 ^T = DSM 115070 ^T), and Duganella rhizosphaerae (type strain R64^T = NBRC 115984 ^T = DSM 115071 ^T) are proposed.