Stimulation of secondary metabolite production in Hypoxylon anthochroum by naturally occurring epigenetic modifiers

Abstract

In pursuit of discovering novel compounds of pharmacological significance, plants and microbes are the potential sources. Endophytic fungi are well-known producers of a myriad class of bioactive metabolites but in laboratory conditions, a substantial number of biosynthetic pathways remain quiescent or under-expressed in conventional culture conditions. Hence, major potential of them is neglected during regular fermentation process. Epigenetic modifiers are reported to modulate fungal genome by altering the expression of metabolite production. Our present study evidences the induction of cryptic secondary metabolite production by Hypoxylon anthochroum, a foliar endophytic fungus of Carica papaya when treated with extracts of garlic and curry leaves. Garlic (Allium sativum), produces allyl mercaptan and diallyl disulfide as the major constituents of organosulfur compounds, which are known to act as inhibitors of histone deacetylases (HDAC). Similarly, Curry leaves (Murraya koenigii) produce mahanine, a carbazole alkaloid, causes DNA methyltransferase (DNMT) inhibition. Hypoxylon anthochroum, when treated with extract of garlic and curry leaves, resulted in 416.12 and 333.33% increase in yield of secondary metabolites, 89% and 85% increase in antioxidant property respectively, along with enhanced antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. High-performance liquid chromatography analysis of the crude extract of H. anthochroum revealed the induction of 19 and 10 new compounds when treated with garlic and curry leaf extracts, respectively, when compared to untreated control. This study suggests that treatment with HDAC inhibitor in the form of garlic extract was more effective than treatment with DNMT inhibitor in curry leaf extract in inducing cryptic metabolites.