Studies on the isolation characterization and bioevaluation of secondary metabolites from Aspergillus Funiculosus Aspergillus Gorakhpurensis and Curvularia Oryzae

Abstract

Microbial diversity serves as potential source for the isolation of bioactive secondary metabolites. Fungi are the most versatile and diversified organisms, exploited for the isolation of therapeutics and agriculturally important metabolites from decades. Indigenous and unexploited fungi serve as a source to isolate new metabolites or known metabolites with new biological activities. In the present thesis, EtoAc extracts of thirty species of fungi indigenously available were evaluated against Gram-positive and negative bacteria for antibacterial activity and larvicidal activity against Spodoptera litura 4th instar larvae. Preliminary screening results reveals that Aspergillus funiculosus, Aspergillus gorakhpurensis and Curvularia oryzae exhibited significantly higher biological activities and warranted for further extensive studies. Chemical structures of the metabolites produced from these fungi were elucidated by 1H, 13C NMR and mass spectral data. Mode of action of the isolated bio active metabolites was established against the bacteria, fungi and S. litura larvae. Kojic acid, 3-phenylpropionic acid and butanoic acid were isolated from A. funiculosus. Antibacterial and antifungal activity of the kojic acid and 3-phenylpropionic acid demonstrated moderate activity against the test bacteria and fungi. Minimum inhibitory concentration (MIC), minimum bactericidal activity (MBC) and time-kill kinetic study results revealed the bacteriostatic nature of the metabolites. Scanning electron microscopic observations of the bacteria treated with metabolites reveals that the metabolites were not induced morphological changes. Moderate antifeedent (DC50= 180.64 and 113.26 Bg/cm2 for kojic acid and 3-phenylpropionic acid respectively) and larvicidal activity (LD50= 693.52 and 381.72Bg/ml respectively) were ascertained against 4th instar S. litura larvae.