Identification of lipopeptides from Bacillus strain Q11 with ability to inhibit the germination of Penicillium expansum, the etiological agent of postharvest blue mold disease

Abstract

The genus Bacillus produces secondary metabolites among which stand out compounds of polypeptide nature for their versatility of applications, one of them is the activity against fungal phytopathogens of agricultural importance. In the present work was evaluated the effectiveness of the crude lipopeptide from Bacillus subtilis Q11 against common soil borne pathogens, additionally in vitro and in vivo assays were carried out to determine the ability to inhibit the germination of conidia and reduce the blue mold rot induced by Penicillium expansum in apple (Malus domestica Borkh) fruit. In antagonistic test, the lipopeptide fraction of Q11 was able to limit the mycelial growth of Rhizoctonia solani, Sclerotium rolfsii, Penicillium expansum, Fusarium stilboides, Colletotrichum gleosporides and Botrytis cinerea, showing higher inhibition at higher lipopeptide concentrations (10, 20, and 30 μg disk−1); however, it was ineffective against Pseudomonas syrigae, Xanthomonas campestris, and Clavibacter michiganensis. On the other hand, the conidia of P. expansum after being exposed to a concentration of 800 mg L−1 of lipopeptide for 16 h, showed swelling and germination reduction greater than 90%. In fruit assay with apples inoculated with a droplet of conidia suspension (200 conidia) of P. expansum, the treatment with the lipopeptide fraction reduced rot lesion severity, registering the greatest effects at 80 μg, which reduced the size of the lesion by more than 60%. The analysis by infrared spectroscopy, HPLC and MALDI-TOF established that the crude lipopeptide is a complex formed primarily by iturin-type compounds with fatty acid chain length of C14–C17 and small proportion of compounds of fengycin A and B type that differ in the length of the fatty acid chain. These compounds could be useful in the development of products for biological control of postharvest blue mold disease in apple.