Diversity and functional characterization of antifungal-producing Streptomyces-like microbes isolated from the rhizosphere of cajuput plants (Melaleuca leucodendron L.)

Abstract

Aims: The study was undertaken to evaluate the diversity of actinomycetes from the rhizosphere of the cajuput plant (Melaleuca leucodendron L.) using ARDRA, and to examine their in vitro antifungal potency against selected fungi. Methodology and results: A total of 78 Streptomyces-like microbes were isolated from the limestone rhizosphere of cajuput plants and cultured in SN agar medium. The ability to inhibit fungal growth was observed using a dual culture assay. The diversity of the isolates was examined by morphological and genotype profiling using ARDRA (Amplified 16S ribosomal DNA restriction analysis), following which they were assigned to eight groups. Seventeen (21.8%) strains showed the ability to produce the antifungal compound as evidenced by their antagonism in vitro against the tested fungi, namely Saccharomyces cerevisiae BY 47420, Candida albicans CGMCC 2538, Aspergillus flavus NRLL 3357, and Fusarium oxysporum KFCC 11363P in the dual culture assay. One isolate, GMR22, which showed potent antagonism against unicellular and filamentous fungi, displayed 97% 16S rRNA sequence similarity to Streptomyces vayuensis. Conclusion, significance and impact of study: This study demonstrated that a diversity of Streptomyces-like antifungal producing microbes were present in the rhizosphere of cajuput plants in the Wanagama Forests of Indonesia. This rhizosphere represents a potential new source of actinomycetes that produce biologically active compounds. One selected strain (GMR22) has the potential to be developed as a commercial biofungicide.