The Effects of Different Antibiotics on Pseudo-nitzschia Diatoms and their Microbial Communities

Christopher McDonald, University of the Virgin Islands, College of Science and Math, St. Thomas, United States Virgin Islands, Rachel Ellen Diner, University of California, San Diego / J. Craig Venter Institute, Scripps Institution of Oceanography, La Jolla, CA, United States, Patrick Brunson, University of California San Diego, San Diego / J. Craig Venter Institute, Scripps Institution of Oceanography, La Jolla, CA, United States and Andrew E Allen, J. Craig Venter Institute, La Jolla, CA, United States
Abstract:
Pseudo-nitzschia diatoms are photosynthetic unicellular algae found in marine habits. This genus produces a toxin known as Domoic Acid (DA) which can cause amnesic shellfish poisoning. While only produced by the diatoms, DA toxins have been found in zooplankton, shellfish, crustaceans, echinoderms, worms, and marine animals. Numerous and diverse bacteria surround Pseudo-nitzschia diatoms, potentially representing a symbiotic relationship. For this project, we tested whether antibiotics could remove bacteria from cultures of three species of Pseudi-nitzschia without impairing diatom growth. We observed Pseudo-nitzschia growth with antibiotics by measuring chlorophyll A fluorescence (a proxy for cell number). We also plated cultures on marine agar plates to determine whether bacteria continued to grow after antibiotic treatment. We found that most antibiotic treatments resulted in breakthrough bacterial growth several days of treatment. One antibiotic treatment eliminated bacteria but also inhibited (either directly or indirectly) diatom growth.
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