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. 2014 Nov 21:5:636.
doi: 10.3389/fmicb.2014.00636. eCollection 2014.

Responses of beneficial Bacillus amyloliquefaciens SQR9 to different soilborne fungal pathogens through the alteration of antifungal compounds production

Bing Li  1 , Qing Li  1 , Zhihui Xu  1 , Nan Zhang  1 , Qirong Shen  1 , Ruifu Zhang  2
Affiliations

Responses of beneficial Bacillus amyloliquefaciens SQR9 to different soilborne fungal pathogens through the alteration of antifungal compounds production

Bing Li et al. Front Microbiol. .

Abstract

Bacillus amyloliquefaciens SQR9 exhibited predominantly antagonistic activities against a broad range of soilborne pathogens. The fungi-induced SQR9 extracts possess stronger antifungal activities compared with SQR9 monoculture extracts. To investigate how SQR9 fine-tunes lipopeptides (LPs) and a siderophore bacillibactin production to control different fungal pathogens, LPs and bacillibactin production and transcription of the respective encoding genes in SQR9 were measured and compared with six different soilborne fungal pathogens. SQR9 altered its spectrum of antifungal compounds production responding to different fungal pathogen. Bacillomycin D was the major LP produced when SQR9 was confronted with Fusarium oxysporum. Fengycin contributed to the antagonistic activity against Verticillium dahliae kleb, Fusarium oxysporum, Fusarium solani, and Phytophthora parasitica. Surfactin participated in the antagonistic process against Sclerotinia sclerotiorum, Rhizoctonia solani, and Fusarium solani. Bacillibactin was up-regulated when SQR9 was confronted with all tested fungi. The reduction in antagonistic activities of three LP and bacillibactin deficient mutants of SQR9 when confronted with the six soilborne fungal pathogens provided further evidence of the contribution of LPs and bacillibactin in controlling fungal pathogens. These results provide a new understanding of specific cues in bacteria-fungi interactions and provide insights for agricultural applications.

Keywords: Bacillus amyloliquefaciens SQR9; bacteria-fungal interaction; lipopeptide antibiotics; soilborne pathogens; transcriptional response.

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Figures

Figure 1
Figure 1
Antimicrobial spectrum of SQR9 with 6 tested soil-borne pathogens. VDK, Verticillium dahliae Kleb; SS, Sclerotinia sclerotiovum (Lib.) de Bary; FOC, Fusarium oxysporum f. sp. cucumerinum; RSK, Rhizoctonia solani Kahn.; FS, Fusarium solani (Mart.)App.etwoll.; and PP, Phytophthora parasitica var.nicotianae (Bredade Hean) Tucker.
Figure 2
Figure 2
Schematic representation of secondary metabolite gene clusters in Bacillus amyloliquefaciens SQR9. Gene clusters encoding non-ribosomal peptide synthetases (NRPSs). The names assigned to individual genes in SQR9 are indicated above the arrows. Products assigned to the respective pathways are shown on the right. GenBank accession numbers in the SQR9 genome are indicated below the arrows.
Figure 3
Figure 3
Antagonistic assay of extractions of the Sfp-deficient mutant SQR9M6 against 6 fungal pathogens. Left, oxford cup containing extraction from SQR9 monoculture. Right, Oxford cup containing extraction from Sfp-deficient mutant SQR9M6. VDK, Verticillium dahliae Kleb; SS, Sclerotinia sclerotiorum; FOC, Fusarium oxysporum; RSK, Rhizoctonia solani (Mart.) App.etwoll; FS, Fusarium solani; and PP, Phytophthora parasitica.
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