The marine diatom Pseudo-nitzschia (PN) produces domoic acid (DA), a neurotoxin that has caused widespread human poisoning along the northeast and northwest coasts of the contiguous U.S. Researchers have investigated many factors thought to stimulate production of DA, but they have not adequately studied bacteria as potential triggers. We are working to understand the biosynthetic machinery of DA in PN and the influence of marine bacteria in the synthesis of DA and related toxins.

Why We Care
Domoic acid (DA) is a neurotoxin that can accumulate in shellfish and can cause Amnesic Shellfish Poisoning in people who eat contaminated shellfish. DA-related poisoning remains a persistent problem on the northeast and northwest coasts of the contiguous U.S.

Several strains of Pseudo-nitzschia (PN), a marine diatom alga, produce DA in both coastal and open ocean waters. First discovered as a human health problem in 1987 after causing illness and death in Prince Edward Island, Canada, scientists have no clear consensus on the environmental triggers for DA production. Researchers have considered several factors that might influence DA production, including nutrient stress, light, salinity, and trace metals (particularly, iron and copper). Some believe that DA biosynthetic production is stimulated by a stress response or in association with slowing or cessation of diatom growth.

Science cannot currently explain the mechanistic relationship between high abundances of naturally occurring epiphytic bacteria (surface dwelling) on PN and significantly higher DA production in PN. Another relevant observation is that bacterial epiphytes on PN do not produce the DA molecule themselves, but direct contact with the PN cells seems required for PN to produce DA.

What We Are Doing
We are:

1. Conducting experiments to assess the diversity of DA molecular structures, which will be new to science and discovered as the research proceeds.
2. Untangling the parallel operation of distinct biosynthetic pathways that must be involved in the synthesis of DA.
3. Unraveling the metabolites involved in the complex interaction between PN and surface-inhabiting bacteria (epiphytes or epibionts), which can lead to better understanding of elevated DA production, both in culture and in natural blooms.
4. Investigating the genes involved in the hybrid biosynthesis of DA, which will provide insights about how diatom–bacteria interactions can regulate biosynthetic processes. This part of the research will also shed light on the role that cellular processes may play in the creation, regulation, and release of DA varieties.
5. Assessing the importance of bacterial influence on PN toxic bloom formation, which can lead to a better understanding of this harmful algal bloom phenomenon and its mitigation.

Important outcomes include:

1. New information about the DA biosynthetic machinery at work, which can lead to better mitigation and management of toxic PN blooms.
2. Understanding the influence of bacteria on toxic PN bloom formation. If a link exists, the information could potentially be used to determine PN bloom toxicity.
3. Integrating project results with other environmental factors to make better predictive models that forecast PN blooms and bloom toxicity.

Dr. Marilou Sison-Mangus leads this project along with co-leads Dr. Philip Crews and Dr. Juhe Lee, all from the University of California Santa Cruz. The project is funded through the NCCOS Ecology and Oceanography of Harmful Algal Bloom (ECOHAB) Program.