Antagonistic effect of chitinolytic Pseudomonas and Bacillus on growth of fungal hyphae and spores of aflatoxigenic Aspergillus flavus

Use of biological control methods has become a promising strategy to counteract deleterious fungal contaminations and substantial post harvest losses. One of the major biological control methods is found in the use of fungal cell wall-degrading enzymes such as chitinases, which hydrolyze the homopolymer of β-1,4-1inked N-acetylglucosamine residues exposed on the fungal cell surface. In this study, antagonistic effects of the chitinolytic enzyme producing isolates of Pseudomonas fluorescens PB27, Bacillus cereus B1 and Bacillus thuringiensis K1 against the aflatoxigenic fungus Aspergillus flavus were investigated. Germination of the spores of A. flavus was inhibited by up to nearly 20% after co-incubation with P. fluorescens PB27 for 72 h, whereas the fungal spores were less affected when incubated with either B. cereus B1 or B. thuringiensis K1. When P. fluorescens or its extracted extracellular enzyme preparation was sprayed on the surface of hazelnuts, the growth of A. flavus was reduced nearly 25%. Scanning electron microscopy observations of hyphae and spores revealed that these enzymes induce numerous ultrastructural morphological changes during spore germination and mycelium growth. Since chitinolytic enzymes have not been shown to be toxic to humans or the environment, based on the observations in this study, an understanding of the functional properties and antagonistic effect of this natural antifungal agent can be practical in the management of post-harvest losses caused by food pathogenic and aflatoxin producing fungi.