Screening the Secondary Metabolites of Caulerpa spp. Surface Associated Bacteria for Antimicrobial Compounds

Antibiotic resistance is on the rise across the globe. New sources of antibiotics are urgently needed. Macroalgae surface-associated bacteria (SAB) are a well-documented source of antimicrobial drug leads. The Carlson Lab has been building a unique collection of these bacteria from Florida and California. We focused our efforts on 87 SAB isolates from the invasive green algae Caulerpa spp.. SAB from our collection were cultivated on A1 agar (10 g starch, 4 g yeast, 2 g peptone, 15 g Instant Ocean, 10 g agar in 500 mL milli-q water) in a grid pattern for 2 days. Slow-growing bacteria or possible contamination from surrounding bacterial growth replated on separate, new grids. A second 1% LB agar containing the human pathogens Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Salmonella sp. was then poured over the top. The second layer was incubated at 37°C overnight. The next day the plates were observed, looking for zones where the bacteria was prevented from growing by the SAB metabolites. We were interested in what percentage of bacteria produced antimicrobial compounds and if the slow and fast-growing bacteria were more or less likely to produce antimicrobial compounds. The results of this preliminary study will be presented.