Characterization of a Bacillus velezensis strain isolated from Bolbostemmatis Rhizoma displaying strong antagonistic activities against a variety of rice pathogens

Abstract

Biological control is an effective measure in the green control of rice diseases. To search for biocontrol agents with broad-spectrum and high efficiency against rice diseases, in this study, a strain of antagonistic bacterium BR-01 with strong inhibitory effect against various rice diseases was isolated from <i>Bolbostemmatis Rhizoma</i> by plate confrontation method. The strain was identified as <i>Bacillus velezensis</i> by morphological observation, physiological and biochemical identification, and molecular characterization by 16S rDNA and <i>gyrB</i> gene sequencing analysis. The confrontation test (dual culture) and Oxford cup assays demonstrated that <i>B. velezensis</i> BR-01 had strong antagonistic effects on <i>Magnaporthe oryzae</i>, <i>Ustilaginoidea virens</i>, <i>Fusarium fujikuroi</i>, <i>Xanthomonas oryzae</i> pv. <i>Oryzicola</i>, and <i>Xanthomonas oryzae</i> pv. <i>oryzae</i>, the major rice pathogens. The genes encoding antimicrobial peptides (<i>ituA</i>, <i>ituD</i>, <i>bmyB</i>, <i>bmyC</i>, <i>srfAA</i>, <i>fenB</i>, <i>fenD</i>, <i>bacA</i>, and <i>bacD</i>) were found in <i>B. velezensis</i> BR-01 by PCR amplification with specific primers. <i>B. velezensis</i> BR-01 could produce protease, cellulase, β-1,3-glucanase, chitinase, indoleacetic acid, siderophore, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and might produce three lipopeptide antibiotics, surfactin, iturin, and fengycin based on Liquid chromatography-mass spectrometry (LC-MS) results. Furthermore, the plant assays showed that <i>B. velezensis</i> BR-01 had significant control effects on rice bacterial blight and bacterial leaf streak by pot experiments in greenhouse. In conclusion, <i>B. velezensis</i> BR-01 is a broad-spectrum antagonistic bacterium and has the potential as the ideal biocontrol agent in controlling multiple rice diseases with high efficiency.