Biocontrol of tomato bacterial wilt by the new strain Bacillus velezensis FJAT-46737 and its lipopeptides

Meichun Chen,Wenjing Yang,Bo Liu,Jieping Wang,Cibin Ge,Zheng Chen,Rongfeng Xiao,Yujing Zhu

doi:10.1186/s12866-020-01851-2

Meichun Chen, Wenjing Yang + Show 6 more

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https://doi.org/10.1186/s12866-020-01851-2

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Abstract

BackgroundThere is an urgent need to discover biocontrol agents to control bacterial wilt. This study reports on a new lipopeptide-producing biocontrol strain FJAT-46737 and explores its lipopeptidic compounds, and this study investigates the antagonistic effects of these compounds.ResultsBased on a whole genome sequence analysis, the new strain FJAT-46737 was identified as Bacillus velezensis, and seven gene clusters responsible for the synthesis of bioactive secondary metabolites in FJAT-46737 were predicted. The antimicrobial results demonstrated that FJAT-46737 exhibited broad-spectrum antimicrobial activities in vitro against three bacteria and three fungi. Pot experiments showed that the control efficiencies for tomato bacterial wilt of the whole cultures, the 2-fold diluted supernatants and the crude lipopeptide of FJAT-46737 were 66.2%, 82.0%, and 96.2%, respectively. The above results suggested that one of the antagonistic mechanisms of FJAT-46737 was the secretion of lipopeptides consisting of iturins, fengycins and surfactins. The crude lipopeptides had significant antagonistic activities against several pathogens (including Ralstonia solanacearum, Escherichia coli and Fusarium oxysporum) and fengycins were the major antibacterial components of the lipopeptides against R. solanacearum in vitro. Furthermore, the rich organic nitrogen sources (especially yeast extracts) in the media promoted the production of fengycin and surfactin by FJAT-46737. The secretion of these two lipopeptides was related to temperature fluctuations, with the fengycin content decreasing by 96.6% and the surfactins content increasing by 59.9% from 20 °C to 40 °C. The optimal temperature for lipopeptide production by FJAT-46737 varied between 20 °C and 25 °C.ConclusionsThe B. velezensis strain FJAT-46737 and its secreted lipopeptides could be used as new sources of potential biocontrol agents against several plant pathogens, and especially the bacterial wilt pathogen R. solanacearum.

Highlights

There is an urgent need to discover biocontrol agents to control bacterial wilt
The phylogenetic analysis of the 16S rRNA and gyrase subunit B (gyrB) gene results indicated that strain FJAT-46737 belongs to the genus Bacillus and is closely related to strains B. velezensis and B. amyloliquefaciens (Figure S3, S4)
Because of the high degree of relatedness among B. amyloliquefaciens, B. siamensis and B. velezensis, the average nucleotide identity (ANI) method based on the whole-genome sequence was used to discriminate strain FJAT-46737

Summary

Introduction

There is an urgent need to discover biocontrol agents to control bacterial wilt. This study reports on a new lipopeptide-producing biocontrol strain FJAT-46737 and explores its lipopeptidic compounds, and this study investigates the antagonistic effects of these compounds. Bacterial wilt caused by Ralstonia solanacearum is a devastating disease that affects almost 250 plant species, and it seriously threaten plant growth and leads to huge losses worldwide [1, 2]. Traditional agricultural practices, such as crop rotation, field sanitation, resistant variety cultivation, and chemical bactericide application, have been widely applied to control the bacterial wilt, they present certain shortcomings [3]. Biological control using antagonistic microorganisms including bacteria, yeasts, and filamentous fungi, represent a safe, effective and sustainable alternative method for fighting plant pathogens compared with chemical bactericides [4,5,6]. The use of alternative antimicobial agents is needed [3, 8]

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