Characterization of Siderophore Produced by Bacillus velezensis YL2021 and Its Application in Controlling Rice Sheath Blight and Rice Blast.

Bacillus velezensis YL2021 has extensive antimicrobial activities against phytopathogens, and its genome harbors a catechol-type siderophore biosynthesis gene cluster. Here, we describe the characterization of siderophore produced by strain YL2021 and its antimicrobial activity in vitro and in vivo. A few types of siderophores were detected by chrome azurol S plates coupled with Arnow's test, purified and identified by Reversed-phase high-performance liquid chromatography (RP-HPLC). We found that strain YL2021 can produce different antimicrobial compounds under low-iron M9 medium or iron-sufficient LB medium although antimicrobial activities can be easily observed on the two media as described above in vitro. Strain YL2021 can produce at least three catechol-type siderophores in low-iron M9 medium while no siderophore was produced in LB medium. Among them, the main antimicrobial siderophore produced by strain YL2021 was bacillibactin, with m/z of 882, based on the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, which has broad-spectrum antimicrobial activities against Gram-positive, Gram-negative bacteria, the oomycete Phytophthora capsici and phytopathogenic fungi. Moreover, the antifungal activity of siderophore including bacillibactin observed in vitro was correlated with control efficacies against rice sheath blight disease caused by Rhizoctonia solani and rice blast disease caused by Magnaporthe oryzae in vivo. Collectively, the results demonstrate that siderophore including bacillibactin produced by Bacillus velezensis YL2021 is a promising biocontrol agent for application in rice disease control.