The rhizosphere, an important battleground between beneficial microbes and pathogens, is usually considered to be a good source for isolation of antagonistic microorganisms. In this study, a novel actinobacteria with broad-spectrum antifungal activity, designated strain NEAU-H2T, was isolated from the rhizosphere soil of wheat (Triticum aestivum L.). 16S rRNA gene sequence similarity studies showed that strain NEAU-H2T belonged to the genus Streptomyces, with high sequence similarities to Streptomyces rhizosphaerihabitans NBRC 109807T (98.8%), Streptomyces populi A249T (98.6%), and Streptomyces siamensis NBRC 108799T (98.6%). Phylogenetic analysis based on 16S rRNA, atpD, gyrB, recA, rpoB, and trpB gene sequences showed that the strain formed a stable clade with S. populi A249T. Morphological and chemotaxonomic characteristics of the strain coincided with members of the genus Streptomyces. A combination of DNA–DNA hybridization results and phenotypic properties indicated that the strain could be distinguished from the abovementioned strains. Thus, strain NEAU-H2T belongs to a novel species in the genus Streptomyces, for which the name Streptomyces triticiradicis sp. nov. is proposed. In addition, the metabolites isolated from cultures of strain NEAU-H2T were characterized by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. One new compound and three known congeners were isolated. Further, genome analysis revealed that the strain harbored diverse biosynthetic potential, and one cluster showing 63% similarity to natamycin biosynthetic gene cluster may contribute to the antifungal activity. The type strain is NEAU-H2T (= CCTCC AA 2018031T = DSM 109825T).
A group of Sesbania cannabina rhizobia belonging to four recA genotypes of a novel group was further characterized in comparison with the related Ensifer species. They showed 98.2 to 99.9 % similarities among themselves and 92.9 to 93.3 % similarities with the most related strain Ensifer sojae CCBAU 05684 T in multilocus sequence analysis of recA, atpD and glnII. The genome average nucleotide identity values between representative strain YIC4027 T and the type strains of its closely related species were 81.6 to 88.9 %. Identical symbiotic gene (nodA, nodC and nifH) sequences highly similar with those in other Sesbania-nodulating strains (Rhizobium sp. SIN-1, Neorhizobium huautlense S02 T , Ensifer saheli ORS609 T and Rhizobium sp. IRBG74) were detected. The representative strain YIC4027 T could form effective nodules on its original host Sesbania cannabina, but not on Sophora flavescens, Trifolium repens, Glycine max, Glycyrrhiza uralensis, Phaseolus vulgaris or Medicago sativa. The use of lactulose as sole carbon source, possession of C 13 : 0 2-OH, C 13 : 1 at 12-13, C 15 : 1 iso !9c, C 17 : 0 anteiso and C 18 : 0 iso and absence of C 14 : 0 anteiso, C 15 : 0 anteiso and C 18 : 0 3-OH in fatty acids distinguished the strain YIC4027 T from the type strains of its closely related species. Based on all the analyses mentioned above, we propose a novel species Ensifer alkalisoli sp. nov. and designate YIC4027 T (=HAMBI 3655 T =LMG 29286 T ) as the type strain. The genome size of YIC4027 T is 5.97 Mbp, comprising 5588 predicted genes, and the DNA G+C content is 62.2 mol%.
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