Natural products have played an important role as drug leads for different diseases. They provide unique structural cores with diverse biological activities. Because of the overuse of antibiotics many pathogens have developed antibiotic-resistance; there is an urgent and continuing need for new antibiotics.

Fungi are a great source for new natural products with diverse biological activities; fungal genomic sequence data have shown that there are more secondary metabolite pathways than known metabolites. To obtain new natural products, an efficient way is needed to access these silent biosynthetic pathways (SBPs). Currently, different strategies have been used to access silent biosynthetic pathways including culture dependent methods like One Strain Many Compound (OSMAC) and co-culture, and genomic-based methods including heterologous expression and promoter activation. All of the above methods have their limitations, which prohibit their broad usage. In our group we have proposed a simple and feasible method for this purpose. Epigenetic regulation is a process commonly used by fungi to regulate biosynthesis. Epigenetic processes may silence/downregulate some secondary metabolite biosynthetic pathways. Small molecular epigenetic modifiers can inhibit epigenetic targets and upregulate gene expression. In this dissertation I have applied this strategy on two fungi and demonstrated that some secondary metabolite pathways can be activated/upregulated by epigenetic modifiers. Chapter 3 and chapter 4 will focus on the description of using small molecules epigenetic modifier (5-azacytidine) to access SBPs. Chapter 3 reports a significant change in the secondary metabolites excreted by an Atlantic-forest-soil-derived Penicillium citreonigrum, which is a rich source of secondary metabolites. Two new metabolites, atlantinones A and B accompanied by eight known compounds were isolated from the guttates. Chapter 4 describes the application of different culture methods let to the production of different secondary metabolites. Waikialoids A and B were isolated from static culture whereas asperonol A and B were from shaking culture. Chapter 5 is different from above chapters and it mainly focuses on the hybrid NRPS-PKS gene coded metabolites, mutanobactin B-D, which are the signal regulators with other microorganisms.