Antagonistic Streptomyces sp and their Metabolites as Biological Control Agents against Fruit Rotting Fungi

Abstract

Actinomycetes strains were isolated from soil of Phoomdi of Loktak lake, Manipur, newlineIndia. Phoomdi soil is explored for the isolation of novel microorganisms due to newlineunique ecological niches and rich biodiversity, because new antibiotics and their newlineproducing microorganisms have been in demand from the health care point of view to newlinecombat the existing and emerging drug resistant pathogens. By the use of selective newlinemedia, 70 actinomycetes strains were isolated from Phoomdi soil and on the basis of newlinemorphological and physiological properties, four actinomycetes isolates i.e. MT7, newlineMT9, MT12 and MT59 were selected and assessed for their in vitro antifungal potential newlineagainst toxigenic fruit-rotting fungi, and among them two potential strains MT7 and newlineMT9 were further studied for their biocontrol potential against various fruit-rotting newlinefungi. newlineAn Indian indigenous antifungal strain MT7 was identified by its cultural newlinecharacteristics, fatty acid methyl ester and 16S rRNA gene analysis which suggested newlinethat strain MT7 belongs to Streptomyces sp. and was found to be identical to newlineStreptomyces violascens. It exhibited broad-spectrum antifungal activity against newlinevarious pathogenic post-harvest fungi of citrus and papaya. Antagonist S. violascens newlineMT7 produced various cell-wall lytic enzymes, including chitinase (8.324 U/ml), and#946;- newline1,3-glucanase (11.246 U/ml) and protease (289.15 U/ml), and these mycolytic newlineenzymes were optimally active at pH 8.0 and 50, 60 and 70 ºC, respectively. In shakeflask newlinefermentation in M93 broth medium, antagonist S. violascens MT7 highly newlineproduced extracellular antifungal metabolites in early stationary growth phase. Both newlineextracellular culture fluid (ECF) and its n-butanol extract showed significant broadspectrum newlinefungal mycelial inhibition of several tested fruit-rotting fungi. Antifungal newlinemetabolite was found to be heat stable, non-peptidic and polyene type antibiotic.