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Antagonistic endophytic bacteria associated with nodules of soybean (Glycine maxL.) and plant growth-promoting properties

Zhao, LongFei, Xu, YaJun, Zheng, Aizhen, Lai, XinHe
Brazilian Journal of Microbiology 2017
Acinetobacter, Glycine max, Ochrobactrum, Phytophthora, Pseudomonas, antagonists, bacteria, endophytes, fungi, genes, hyphae, indole acetic acid, microscopy, mycelium, nitrogen fixation, phylogeny, protoplasts, regression analysis, ribosomal RNA, root nodules, seedlings, siderophores, soybeans, China
A total of 276 endophytic bacteria were isolated from the root nodules of soybean (Glycine max L.) grown in 14 sites in Henan Province,China.The inhibitory activity of these bacteria against pathogenic fungus Phytophthora sojae01 was screened in vitro. Six strains with more than 63% inhibitory activities were further characterized through optical epifluorescence microscopic observation, sequencing, and phylogenetic analysis of 16S rRNA gene, potential plant growth-promoting properties analysis, and plant inoculation assay. On the basis of the phylogeny of 16S rRNA genes,the six endophytic antagonists were identified as belonging to five genera:Enterobacter, Acinetobacter, Pseudomonas, Ochrobactrum, and Bacillus.The strain Acinetobacter calcoaceticusDD161 had the strongest inhibitory activity (71.14%) against the P. sojae01, which caused morphological abnormal changes of fungal mycelia; such changes include fracture, lysis, formation of a protoplast ball at the end of hyphae, and split ends. Except for Ochrobactrum haematophilum DD234, other antagonistic strains showed the capacity to produce siderophore, indole acetic acid, and nitrogen fixation activity. Regression analysis suggested a significant positive correlation between siderophore production and inhibition ratio against P. sojae01. This study demonstrated that nodule endophytic bacteria are important resources for searching for inhibitors specific to the fungi and for promoting effects for soybean seedlings.