Bacterial Community of Water Yam (Dioscorea alata L.) cv. A-19.

The bacterial community of water yam (Dioscorea alata L.) cv. A-19 is vital because it may promote plant growth without the need for fertilization. However, the influence of fertilization practices on the composition and proportion of the bacterial community of water yam cv. A-19 has not yet been extensively examined. Therefore, we herein investigated the diversity and composition of the bacterial community of water yam cv. A-19 cultivated with and without chemical fertilization using amplicon community profiling based on 16S rRNA gene sequences. No significant difference was detected in the growth of plants cultivated with or without chemical fertilization. Alpha diversity indices were significantly dependent on each compartment, and a decrease was observed in indices from the belowground (rhizosphere and root) to aboveground compartments (stem and leaf). The bacterial composition of each compartment was clustered into three groups: bulk soil, rhizosphere and root, and stem and leaf. Chemical fertilization did not significantly influence the diversity or composition of the water yam cv. A-19 bacterial community. It remained robust in plants cultivated with chemical fertilization. The amplicon community profiling of bacterial communities also revealed the dominance of two bacterial clades, the Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade and Burkholderia-Caballeronia-Paraburkholderia clade, with and without chemical fertilization. This is the first study to characterize the bacterial community of water yam cv. A-19 cultivated with and without chemical fertilization.

Rhizobium dioscoreae sp. nov., a plant growth-promoting bacterium isolated from yam (Dioscorea species).

This study investigated endophytic nitrogen-fixing bacteria isolated from two species of yam (water yam, Dioscorea alata L.; lesser yam, Dioscorea esculenta L.) grown in nutrient-poor alkaline soil conditions on Miyako Island, Okinawa, Japan. Two bacterial strains of the genus Rhizobium, S-93T and S-62, were isolated. The phylogenetic tree, based on the almost-complete 16S rRNA gene sequences (1476 bp for each strain), placed them in a distinct clade, with Rhizobium miluonense CCBAU 41251T, Rhizobium hainanense I66T, Rhizobium multihospitium HAMBI 2975T, Rhizobium freirei PRF 81T and Rhizobium tropici CIAT 899T being their closest species. Their bacterial fatty acid profile, with major components of C19 : 0 cyclo ω8c and summed feature 8, as well as other phenotypic characteristics and DNA G+C content (59.65 mol%) indicated that the novel strains belong to the genus Rhizobium. Pairwise average nucleotide identity analyses separated the novel strains from their most closely related species with similarity values of 90.5, 88.9, 88.5, 84.5 and 84.4 % for R. multihospitium HAMBI 2975T, R. tropici CIAT 899T, R. hainanense CCBAU 57015T, R. miluonense HAMBI 2971T and R. freirei PRF 81T, respectively; digital DNA-DNA hybridization values were in the range of 26-42 %. Considering the phenotypic characteristics as well as the genomic data, it is suggested that strains S-93T and S-62 represent a new species, for which the name Rhizobium dioscoreae is proposed. The type strain is S-93T (=NRIC 0988T=NBRC 114257T=DSM 110498T).