Bacillus velezensis JJYY against soil-borne diseases: biocontrol effect, whole genome sequencing, and antimicrobial components

Abstract:

[Background] Soil-borne diseases are a key factor limiting the agriculture sustainable development in the world and become increasingly serious in vegetables and Chinese medicinal herbs in China, leading to critically continuous-cropping obstacles. Biocontrol of soil-borne diseases, without causing safety problems to the environment and agricultural products, is a hot research topic. [Objective] To identify the strain JJYY with a broad antimicrobial spectrum to soil-borne pathogens, evaluate its control effects on major soil-borne diseases, and identify its major antimicrobial metabolic products. [Methods] This strain was identified by a combination of morphological observation with scanning electron microscopy, physiological and biochemical tests, and 16S rRNA gene sequencing. Turbidimetry and mycelial growth inhibition assay were employed to determine the EC₅₀ of this strain against four soil-borne bacterial pathogens and five fungal pathogens, respectively. Pot experiments were carried out to evaluate the control effects of the strain on tomato bacterial wilt and other diseases. Illumina NovaSeq and PacBio Sequel were used for whole genome sequencing of this strain, followed by functional annotation in PGAP. Preparative reversed-phase liquid chromatography (prep-RPLC) and mass spectrometry (MS) were employed to isolate and identify the metabolites of this strain. [Results] The strain JJYY was identified as Bacillus velezensis. The EC₅₀ values of the extract of this strain against four soil-borne bacterial pathogens and five soil-borne fungal pathogens were 0.940-1.092 mg/mL and 2.733-3.678 mg/mL, respectively. The strain showed the highest control effects of 80.00%-87.74% on tomato bacterial wilt, Chrysanthemum morifolium root rot, and capsicum Fusarium wilt, with no significant difference compared with streptomycin or hymexazol (P>0.05). The whole genome of this strain was 3 929 792 bp in length, carrying 3 895 genes. The genome of this strain shared 3 445 and 2 997 homologous genes with B. velezensis JS25R and B. subtilis 168, respectively. Twelve gene clusters were predicted to be associated with the synthesis of secondary metabolites. A total of 9 antimicrobial components were separated from the extract of this strain, of which two were preliminarily identified as macroactin D and 7-O-malonyl-macroactin A. [Conclusion] B. velezensis JJYY demonstrates definite control effects on both soil-borne bacterial and fungal diseases, with the genome distinct from reported B. velezensis strains. It produces diverse known and possible novel antibiotics. Identifying the antimicrobial substances and deciphering the antimicrobial mechanisms of this strain would facilitate the development of novel effective biocontrol agents.