Characterization of allelopathic compounds from the red tide dinoflagellate Karenia brevis

Blooms and cultures of the red tide dinoflagellate Karenia brevis exude compounds that inhibit the growth of competing phytoplankton, but the identities of these compounds are unknown. We characterized allelopathic compounds from K. brevis using a variety of chromatographic and spectroscopic techniques. K. brevis produces multiple compounds that are inhibitory towards the Gulf of Mexico diatom Asterionellopsis glacialis. However, brevetoxins, potent neurotoxins responsible for massive fish kills and neurotoxic shellfish poisoning in humans, had no effect on A. glacialis growth. We determined that most allelopathic compounds produced by K. brevis are unstable, polar, organic molecules produced at low concentrations, which are either neutral or positively charged. K. brevis also produces a suite of less polar, but more stable compounds that are moderately allelopathic towards A. glacialis. Given that K. brevis encounters a variety of competitor species in the field, the production of multiple allelopathic compounds could provide a broader chemical arsenal to successfully inhibit these competitors. The allelopathic compounds characterized in more detail had molecular weights between 500 and 1000. Da and possessed aromatic functional groups. Metabolic fingerprinting of K. brevis extracts has not yet led to identification of specific compound(s) responsible for allelopathy. Our results indicate that the ability of K. brevis to outcompete co-occurring phytoplankton may be facilitated by the production of multiple allelopathic compounds.