Abstract
Diethyl sulfate (DES)-based chemical mutagenesis was applied on different fungal strains with the aim of diversifying the secondary metabolites. The mutant strain (VRE-MT1) of Penicillium oxalicum was subjected to dereplication (LCMS-based) and isolation of natural products, resulting in obtaining 10 molecules of bioactive potential. Metabolites, viz. tuckolide, methylpenicinoline, 2-acetyl-3,5-dihydroxy-4,6-dimethylbenzeneacetic acid, penicillixanthone A, brefeldin A 7-ketone, and antibiotic FD 549, were observed for the first time from P. oxalicum. The results of antimicrobial activity reveal that the compounds N-[2-(4-hydroxyphenyl)ethenyl]formamide, methylpenicinoline, and penipanoid A have potent antibacterial activity against Bacillus subtilis (ATCC 6633) with minimum inhibitory concentration (MIC) values of 16, 64, and 16 μM, respectively, and the compounds N-[2-(4-hydroxyphenyl)ethenyl]formamide, methylpenicinoline, and penipanoid A were found active against Escherichia coli (ATCC 25922), with MIC values of 16, 64, and 16 μM, respectively. Also, the metabolites N-[2-(4-hydroxyphenyl)ethenyl]formamide and tuckolide showed effective antioxidant activity in 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid scavenging assays. The mutant VRE-MT1 was found to have 8.34 times higher quantity of N-[2-(4-hydroxyphenyl)ethenyl]formamide as compared to the mother strain. The DES-based mutagenesis strategy has been found to be a potent tool to diversify the secondary metabolites in fungi.