DISCOVERING NOVEL NATURAL PRODUCTS FROM BIOACTIVE PLANTS AND BACTERIA BY

ii Microorganisms and plants have evolved to produce a myriad array of natural products that are of biomedical importance. One group of valuable natural products is polyketides, which are known to be antiviral, antibacterial, and anticancer. In my first project, I attempted to develop an efficient strategy for cloning and characterizing Type III PKS genes that are likely responsible for the synthesis of novel natural products from Eucalyptus species. Nested degenerate primers were designed and a total of 94 clones and 27 clones were sequenced from the cDNA libraries created from the leaves of E. camaldulensis and E. robusta, respectively. Five unique putative Type III PKSs genes were identified. Two full-length genes were cloned and the biochemical characterization of these genes indicated their functions. In my second project, I attempted to develop a synthetic biology approach for natural product discovery. Investigation into the unknown compounds synthesized by actinomycetes may lead to the discovery of novel chemotherapeutic agents. As proof of concept, one cryptic pathway from Streptomyces griseus, containing a PKS/NRPS hybrid gene, was chosen as a model system. To decipher this cluster, I have been attempting to develop a new strategy based on our recently developed “DNA assembler ” method. By using this approach, the gene cluster was modified by adding different constitutive promoters in front of each gene. RT-qPCR was employed to track expression on the transcription level. HPLC and LC-MS were used to detect the products. A potential product was detected and further characterization is in progress. ii