NIEHS-funded researchers have unmasked the genetic basis by which one form of harmful algal bloom becomes toxic. In a study published in the journal Science, a team of researchers identified, for the first time, a cluster of genes associated with producing domoic acid, which is a neurotoxin that makes certain algal blooms harmful to humans and marine life.
The team involved researchers from the Scripps Institution of Oceanography at the University of California at San Diego (UCSD) and the J. Craig Venter Institute. NIEHS grantee Bradley Moore, Ph.D., from Scripps, is the senior author. NIEHS and the National Science Foundation jointly funded the research.
Domoic acid — a neurotoxin
Harmful algal blooms can sicken marine mammals and threaten human health through several means. Single-celled algae, or diatoms, in the genus Pseudo-nitzschia produce domoic acid, which accumulates in the food web. A high-dose exposure to domoic acid can lead to amnesic shellfish poisoning, a potentially fatal condition in humans characterized by seizures and short-term memory loss.
Researchers are eager to understand more about these algal blooms because long-term, low-level consumption of domoic acid can also have serious health effects, including kidney damage or altered fetal development.
First step in forecasting
“Discovery of the genes coding for the synthesis of domoic acid represents a major breakthrough towards more accurate forecasting of toxic algal bloom events,” said Fred Tyson, Ph.D., program director for the NIEHS Oceans and Human Health Program.
With the genes that encode for domoic acid identified, researchers will be able to ask further questions about which oceanic conditions activate the genes and make the blooms toxic, according to a press release from Scripps, written by Lauren Fimbres Wood.
“This work allows scientists to learn more about the oceanographic, geochemical, and geophysical conditions that are associated with the switching on and off of toxin producing genes,” Tyson explained.
Prime conditions becoming more prevalent
To conduct the study, the scientists grew microalgae in culture under conditions that were previously shown to produce the toxin — phosphate limitation and increased carbon dioxide levels.
“[That] finding was significant in part because scientists have observed that the oceans have been taking on additional amounts of carbon dioxide beyond natural levels due to societal use of fossil fuels,” Wood wrote. “This and rising ocean temperatures mean that domoic acid events are becoming more prevalent, more toxic, and lasting longer than in previous decades.”
Next, the team studied the toxic cultured algae using RNA sequencing, which is a method used to identify genes that are expressed. By finding which genes are turned on during neurotoxin production, the researchers could connect the various oceanic conditions that drive algal blooms to develop toxins.
“Because the genomes of the algae are so complex, the biosynthetic pathways for marine microalgal toxins have remained elusive for quite some time,” Moore said in the press release. “Now that we have both a genome for Pseudo-nitzschia and a genetic pathway for domoic acid production, we are beginning to understand why these algae make a toxin and how that capability is activated,” he continued. “This new knowledge may ultimately better educate us how to predict and prepare for future toxic events.”
Citation: Brunson JK, McKinnie SMK, Chekan JR, McCrow JP, Miles ZD, Bertrand EM, Bielinski VA, Luhavaya H, Oborník M, Smith GS, Hutchins DA, Allen AE, Moore BS. 2018. Biosynthesis of the neurotoxin domoic acid in a bloom-forming diatom. Science 361(6409):1356−1358.
Sun J, Hutchins DA, Feng Y, Seubert EL, Caron DA, Fu FX. 2011. Effects of changing pCO2 and phosphate availability on domoic acid production and physiology of the marine harmful bloom diatom Pseudo-nitzschia multiseries. Limnol Oceanogr 56(3):829–840.
(Sheena Scruggs, Ph.D., is the Digital Outreach Coordinator in the NIEHS Office of Communications and Public Liaison.)