Draft Genome Sequences of Chryseobacterium artocarpi UTM-3T and Chryseobacterium contaminans C26T, Isolated from Rhizospheres, and Chryseobacterium arthrosphaerae CC-VM-7T, Isolated from the Feces of a Pill Millipede

Wheat Rhizosphere-Derived Bacteria Protect Soybean from Soilborne Diseases

Soybean (Glycine max [L.] Merr.) is an important oilseed crop with a high economic value. However, three damaging soybean diseases, soybean cyst nematode (SCN; Heterodera glycines Ichinohe), Sclerotinia stem rot caused by the fungus Sclerotinia sclerotiorum (Lid.) de Bary, and soybean root rot caused by Fusarium spp., are major constraints to soybean production in the Great Plains. Current disease management options, including resistant or tolerant varieties, fungicides, nematicides, and agricultural practices (crop rotation and tillage), have limited efficacy for these pathogens or have adverse effects on the ecosystem. Microbes with antagonistic activity are a promising option to control soybean diseases with the advantage of being environmentally friendly and sustainable. In this study, 61 bacterial strains isolated from wheat rhizospheres were used to examine their antagonistic abilities against three soybean pathogens. Six bacterial strains significantly inhibited the growth of Fusarium graminearum in the dual-culture assay. These bacterial strains were identified as Chryseobacterium ginsengisoli, C. indologenes, Pseudomonas poae, two Pseudomonas spp., and Delftia acidovorans by 16S rRNA gene sequencing. Moreover, C. ginsengisoli, C. indologenes, and P. poae significantly increased the mortality of SCN second-stage juveniles (J2), and two Pseudomonas spp. inhibited the growth of S. sclerotiorum in vitro. Further growth chamber tests found that C. ginsengisoli and C. indologenes reduced soybean Fusarium root rot disease. C. ginsengisoli and P. poae dramatically decreased SCN egg number on SCN-susceptible soybean 'Williams 82'. Two Pseudomonas spp. protected soybean plants from leaf damage and collapse after being infected by S. sclerotiorum. These bacteria exhibit versatile antagonistic potential. This work lays the foundation for further research on the field control of soybean pathogens.

Chryseobacterium cucumeris sp. nov., an endophyte isolated from cucumber (Cucumis sativus L.) root, and emended description of Chryseobacterium arthrosphaerae

The Gram-stain-negative, yellow-pigmented, rod-shaped bacterial strain GSE06^T, isolated from the surface-sterilized root of a cucumber plant grown in a field in Gunsan, Korea, was characterized by not only cultural and morphological features but also physiological, biochemical and molecular analyses. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain GSE06^T was most closely related to species of the genus Chryseobacterium. Furthermore, strain GSE06^T exhibited the highest sequence similarities with the type strains Chryseobacterium indologenes ATCC 29897^T (98.9 %), Chryseobacterium gleum ATCC 35910^T (98.8 %), Chryseobacterium arthrosphaerae CC-VM-7^T (98.7 %), Chryseobacterium contaminans C26^T (98.5 %), Chryseobacterium artocarpi UTM-3^T (98.3 %), and Chryseobacterium gallinarum 100^T (97.9 %). Average nucleotide identity values between genome sequences of strain GSE06^T and the above-mentioned reference strains ranged from 81.2 to 86.9 %, which were lower than the threshold of 95 % (corresponding to a DNA-DNA reassociation value of 70 %). The DNA G+C content of strain GSE06^T was 36.1 mol%; the predominant respiratory quinone of the strain was MK-6. The major fatty acids were iso-C15 : 0, summed feature 9 (iso-C17 : 1ω9c), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and iso-C17 : 0 3-OH. The major polar lipids were phosphatidylethanolamine, three aminolipids, one aminophospholipid, four glycolipids and one unidentified lipid. These results of phenotypic and genotypic characteristics could differentiate strain GSE06^T from closely related type strains belonging to the genus Chryseobacterium. Thus, strain GSE06^T is proposed as a representative of a novel species in the genus Chryseobacterium, Chryseobacterium cucumeris sp. nov. The type strain is GSE06^T (=KACC 18798^T=JCM 31422^T).