Iturin A is the principal inhibitor in the biocontrol activity of Bacillus amyloliquefaciens PPCB004 against postharvest fungal pathogens.
OBJECTIVE
A Bacillus amyloliquefaciens strain, surviving epiphytically on the surface of fruit, was isolated while searching for naturally occurring biological control agents. This bacterial strain was characterized for its antifungal activity against seven selected fungal postharvest pathogens of citrus.


RESULTS
To understand the antifungal activity, seven postharvest fungal pathogens were screened for growth inhibition by B. amyloliquefaciens strain. Assays using B. amyloliquefaciens lipopeptide extracts showed a strong inhibitive activity. The inhibitory effect was observed in abnormal conidial germination and germ tube development when conidia were treated with different lipopeptide extract concentrations. Further analysis using PCR and chromatography confirmed the presence of fengycin, iturin and surfactine, of which iturin A showed the strongest and most common inhibitory effect. The results are supported by site-directed mutagenesis analysis, targeted to suppress the biosynthesis of iturin A production. Fruit trials confirmed disease development inhibition when the antagonist was applied 1 day prior to or 1 day after fungal application.


CONCLUSIONS
We conclude that the iturin family of lipopeptides are vital in the antagonism of B. amyloliquefaciens against the seven citrus postharvest pathogenic fungi tested.


CONCLUSIONS
We elucidated the principal mechanism used by B. amyloliquefaciens PPCB004 to suppress postharvest disease development on stored fruits.
Arrebola
E
E
Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria, South Africa.
Jacobs
R
R
Korsten
L
L
D000898:Antibiosis; D000935:Antifungal Agents / Q000302:isolation & purification / Q000494:pharmacology*; D001407:Bacillus / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D002957:Citrus / Q000382:microbiology; D005638:Fruit / Q000382:microbiology; D018525:Germination / Q000187:drug effects; D055666:Lipopeptides / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D003904:Mitosporic Fungi / Q000187:drug effects*; D016297:Mutagenesis, Site-Directed; D010456:Peptides, Cyclic / Q000302:isolation & purification / Q000494:pharmacology*; D010935:Plant Diseases / Q000517:prevention & control; D016133:Polymerase Chain Reaction / Q000379:methods; D013172:Spores, Fungal / Q000187:drug effects
D000935:Antifungal Agents; D055666:Lipopeptides; D010456:Peptides, Cyclic; C049972:fengycin; C013579:iturin A