The Carlson Lab Fraction Library for Secondary Metabolite Screening of Marine Bacteria

Actinomycetes and cyanobacteria are prolific producers of secondary metabolites commonly found in natural product libraries. The Carlson Lab Fraction Library contains fractionated chemical extracts from bacterial and fungal strains isolated from aquatic environments. These extracts are organized in 96-well plates for long-term storage and efficient bioassay testing. Approximately 300 crude extracts have been prepared by liquid-liquid partitioning of culture media with ethyl acetate. For actinomycetes and cyanobacteria, the crude extract is fractionated over silica gel column chromatography, with four different solvent mixtures used to elute different compounds according to their polarity. Each fraction or partition is dried and weighed, and a 7.5 mg subsample is dissolved in DMSO at 10 mg/mL for cryopreservation in an indexed 96-well plate at -20°C. This library has amassed 650 extracts and fractions, enabling rapid bioassay testing without requiring sample preparation each time an assay is executed. Undergraduates here at Pacific have screened for antibiotic activity against 4 human pathogens and, through a collaboration with UC Merced, testing against a panel of human pathogenic fungi is underway. By facilitating high-throughput biological testing and analysis of natural product fractions, the creation of this library is instrumental in our search for novel bioactive compounds.