Inhibitory Activities of Surface-Associated Bacteria from California and Florida Algae
Faculty Mentor Name
Skylar Carlson
Research or Creativity Area
Natural Sciences
Abstract
Marine algal surface-associated bacteria (SAB) inhabit highly competitive and diverse marine environments, where they face various stressors, including high salinity, osmotic pressure, and UV radiation. In response, these bacteria produce secondary metabolites that may function as chemical defenses, including potential antibiotics active against human pathogens. In this study, we isolated and evaluated SAB from marine algae collected on two U.S. coasts, comprising 332 California isolates and approximately 200 Florida isolates. We screened these isolates for antibacterial activity against four clinically prevalent pathogens–Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Salmonella sp.–using pour-over assays for on-plate inhibition, Kirby-Bauer disk diffusion for extract activity, and a single-dose broth assay for liquid-phase confirmation. The 15 active strains were scaled in A1 medium, their metabolites were captured with XAD-16 resin, and the determination of the minimum inhibitory concentrations following solvent partitioning yielded 3 active fractions. The 3 active ethyl acetate fractions were then analyzed by HPLC and LC-MS, and phylogenetic identification was performed using 16S rRNA gene sequencing and Sanger sequencing. Altogether, this workflow provides a systematic analysis of algal SAB antibacterial activity and establishes a pipeline for the discovery of new secondary metabolites.
Inhibitory Activities of Surface-Associated Bacteria from California and Florida Algae
Marine algal surface-associated bacteria (SAB) inhabit highly competitive and diverse marine environments, where they face various stressors, including high salinity, osmotic pressure, and UV radiation. In response, these bacteria produce secondary metabolites that may function as chemical defenses, including potential antibiotics active against human pathogens. In this study, we isolated and evaluated SAB from marine algae collected on two U.S. coasts, comprising 332 California isolates and approximately 200 Florida isolates. We screened these isolates for antibacterial activity against four clinically prevalent pathogens–Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Salmonella sp.–using pour-over assays for on-plate inhibition, Kirby-Bauer disk diffusion for extract activity, and a single-dose broth assay for liquid-phase confirmation. The 15 active strains were scaled in A1 medium, their metabolites were captured with XAD-16 resin, and the determination of the minimum inhibitory concentrations following solvent partitioning yielded 3 active fractions. The 3 active ethyl acetate fractions were then analyzed by HPLC and LC-MS, and phylogenetic identification was performed using 16S rRNA gene sequencing and Sanger sequencing. Altogether, this workflow provides a systematic analysis of algal SAB antibacterial activity and establishes a pipeline for the discovery of new secondary metabolites.
