Organisms use chemicals as a means of interacting with their surroundings and scientists have exploited this fact to discover the vast majority of pharmaceuticals used to treat disease today. Dictyostelium discoideum exhibits the largest repository of polyketide synthase (PKS) enzymes of all known genomes. Furthermore, some types of PKSs in this organism are fused to other enzymatically active protein domains. The unique hybrid arrangement works with great efficiency to synthesize polyketide molecules that are involved in the differentiation of slime mold cells. This has potential implications for the treatment of infectious disease because most of the common antibiotics in clinical use are polyketides derived from soil-borne microbes - however, amoebae have not been examined in this regard. We will begin screening a large archive of soil- borne amoebae for the production of antibiotics. The late Dr. Kenneth Raper, an authority on the ecology and phylogeny of social amoebae, amassed this resource. The Raper Archive is a diverse collection of social soil- borne amoebae representing five different genera, seventeen different species, and over a thousand unique isolates. In this project, co-cultures of dictyostelids and their bacterial prey will be grown in solid or liquid media and the supernatants of these co-cultures will be screened for antimicrobial activity using a panel of known pathogens. The panels will also be grown both in liquid and on solid media. Bioassays will be conducted to identify supernatants that contain antibacterial activity. By using membrane filters with a molecular weight cutoff (5 x 103), we will assess whether the antibiotic function is proteinaceous or small molecule-dependent. Purification procedures will be designed according to the inferred nature of the antibiotic. Our R21 project will reinvigorate pharmaceutical NP research by directing proven antibiotic discovery strategies to target a new and promising source of microbial secondary metabolites, eukaryotic soil-dwelling amoebae. In the short term, this research will improve our scientific knowledge of the functional genomics of dictyostelids. And ultimately, our work will identify lead compounds for much-needed antibiotics that may have novel chemical structures and mechanisms of action.
The growing problem of antibiotic resistance is generating a need for vigorous drug discovery research. Most clinical antibiotics come from screens of soil-dwelling bacteria, which are renowned for their production of valuable metabolites, but are increasingly yielding previously discovered antibiotics. In this antibiotic discovery project we will screen an untapped group of microorganisms with similar ecological and biochemical characteristics to the prolific producers of yesterday: the soil-dwelling, eukaryotic social amoebae.