Screening and activity of yeast-associated with cocoa-bean fermentation against phytopathogenic yeast and fungi

Abstract

Cocoa-bean fermentation has been associated with the involvement of diverse microbial assemblages which consist of a wide array of bacteria and yeast. We attempted to screen and to identify the potential antifungal yeast from this assemblage against phytopathogenic fungi. We employed in-vitro antagonism assay using agar plug methods to performpreliminary screening from 35 yeast isolates followed by total protein production and measurement with Bradford methods. We found three yeast strains that were effective against Trichoderma sp. T009, and two moulds associated with cocoa (Penicilliumsp. Cocoa2 and Fusariumsp.Cocoa 1). The three bioactive yeast strains were identified as Saccharomyces cerevisiae IDI-002, Hanseniasporauvarum IDE-056 and Hanseniasporauvarum IDE-271 based on molecular identification and phylogenetic analysis. The production of antifungal protein from pure cultures on YEPG media resulted intotal protein concentration between 6.20 - 8.17 mg/L. Cell suspension showed higherinhibitory activity compared to thecell-free supernatant gave indication that antifungal proteins in the bulk fermentation was below the minimal inhibitory concentration to cause the inhibitory effect. Further characterization, purification, and optimization are still needed before the up-scale production of antifungal metabolites and its biological control application.