Optimization and characterization of antifungal metabolite from a soil actinomycete <em>Streptomyces indiaensis</em> SRT1

Abstract

A total of 77 soil actinomycete isolates were screened for antifungal activity by cross streak method and agar well diffusion assay. The potential producer strain AI-32 was identified as <em>Streptomyces indiaensis</em> SRT-1 based on its morphological, cultural and physiological characteristics and 16S rRNA gene sequencing. The antifungal metabolite from AI-32 was extracted with organic solvents and purified by column chromatography. Its structure was elucidated by UV, FTIR, NMR and LC-MS analysis and was found to contain an aromatic ring fused with a furan ring linked by ester linkages. The culture conditions for the production of antifungal metabolite were optimized by using various physical and chemical parameters. The optimization studies revealed soybean casein digest supplemented with 1% dextrose (SCDD) broth as the suitable production medium, pH as 8.5, temperature (30^oC), salinity (2%), and incubation period as 8 days and glucose and soybean meal as suitable carbon and nitrogen sources, respectively. Based on the minimum inhibitory concentration and minimum fungicidal concentration values, <em>Fusarium oxysporum </em>(NCIM 1072) was found to be more sensitive test pathogen. The effect of antibiotic on spore germination and mycelial development of <em>F. oxysporum</em> was determined in terms of delayed spore germination, appearance of segmented mycelium and ruptured and distorted spores. This study is the first report highlighting the significance of <em>S. indiaensis</em> produced metabolite as a promising antifungal agent.