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The extent of the pseudo-nitzschia of the Pacific Northwest blossoms in 2015. The gradation of colors in the oceanic areas of purple-blue-green-yellow-red-pink shows a growing concentration of chlorophyll to the coast. Satellite data is courtesy of NASA's Ocean Biology Treatment Group and LAADS-DAAC. Credit: Mati Kahru, Scripps Institution of Oceanography, UC San Diego.
A team led by scientists from the Scripps Institution of Oceanography at the University of California at San Diego and the J. Craig Venter Institute (JCVI) has discovered the genetic basis for the production of domoic acid, a potent neurotoxin produced by harmful algal blooms.
Harmful algal blooms are causing significant economic and environmental damage to coastal communities around the world. These proliferations occasionally produce toxins that can make marine mammals ill and threaten human health when toxins accumulate in seafood. A high-dose exposure to domoic acid, produced by a type of Phytoplankton, known as diatoms of the genus Pseudo-nitzschia, can lead to amnesic intoxication by molluscs, a potentially fatal disease characterized by short-term seizures and short-term memory loss.
In a new study published in the September 28 edition of ScienceThe team of UC San Diego and JCVI scientists identified a group of genes associated with the production of domoic acid toxin in the marine pseudo-nitzschia of phytoplankton.
This type of microalga is remarkable because, in the summer of 2015, it caused the largest harmful algal bloom ever recorded off the west coast of North America, from Alaska to Santa Barbara, and intoxication by shells.
Microscopic view of diatomite-producing pseudo-nitzschia domoic acid in a seawater sample from Monterey Bay, California. This actively growing diatom species usually forms long chains of individual cells. Credit: G. Jason Smith at Moss Landing Marine Labs.
Despite decades of research on pseudo-nitzschia, the molecular basis for the toxicity of these phytoplankton was not known. Scientists have discovered that these newly discovered genes contain biological instructions for making the toxin and are then "activated" when Pseudo-nitzschia produces domoic acid.
"By identifying genes that code for domoic acid production, we can now ask about the different ocean conditions that activate or deactivate genes," said Scripps Institution of Oceanography and JCVI Ph.D. student Patrick Brunson, one of the two main authors of the study. "This knowledge will allow us to track the evolution of proliferation toxicity at the genetic level."
By showing how domoic acid production genes are activated in culture, the authors suggest a way to relate ocean conditions to the origin of the evolution of algal blooms to development. toxin production.
"It is extremely important to understand how algae proliferate and what conditions are responsible," said Hedy Edmonds, program director at the Division of Ocean Sciences at the National Science Foundation, which partly funded the research. "This study provides a possible tool for monitoring algal blooms and predicting toxin production before it occurs."
Harmful algal blooms are difficult to predict and proliferation organisms usually have large, highly complex genomes. The authors of the study argue that the greatest implication will be the ability to look at a proliferation at the genetic level. Knowing the genes involved in domoic acid production will allow for genetic monitoring of algal blooms and help identify conditions that trigger toxin production.
"Because the genomes of the algae are so complex, the pathways of marine microalgae toxin biosynthesis have remained unresolved for some time," said lead author Bradley Moore, a chemist and geneticist from Scripps and Skaggs. School of Pharmaceuticals. . "Now that we have both a genome for pseudo-nitzschia and a genetic pathway for domoic acid production, we begin to understand why these microalgae are a toxin and how that ability is activated. future toxic events. "
This work has advanced research conducted in 2011 by David Hutchins of the University of Southern California, also co-author of this study, who found that when phosphates are limited and the amount domoic acid and become harmful. The results were significant in part because scientists have observed that the oceans absorb additional amounts of carbon dioxide beyond natural levels due to society's use of fossil fuels. This and rising ocean temperatures mean that domoic acid events are becoming more frequent, more toxic and last longer than previous decades. Scripps researchers used the results of the Hutchins study to identify the genes responsible for producing this toxin.
"We found it very interesting that the combination of phosphate limitation and the increase of carbon dioxide could have such a powerful but nuanced effect on domoic acid production in culture," said Andrew E. Allen, Diatom and Genomics Specialist at Scripps. JCVI who is also a senior author of the study. "We could directly correlate gene expression to toxin production, and this observation led us directly to the genes encoding domoic acid."
Scripps and Patrick Brunson, graduate student of JCVI, pipettes. Pseudo-nitzschia diatoms at the Andrew Allen Lab of the J. Craig Venter Institute. Credit: J. Craig Venter Institute
JCVI researchers working on Allen's lab have extracted and sequenced RNA transcripts from microalgae, an approach that measures active genes. Subsequent analysis of the genetic sequences encoded by the RNA transcripts identified the genes believed to produce the toxins. In vitro biochemistry experiments conducted in Moore's lab at Scripps then established a series of enzymes that create the central structure of the toxin.
"Some of the biosynthetic enzymes of domoic acid that build this toxin are unique at the genetic and biochemical level," said Shaun McKinnie, a postdoctoral researcher at Scripps and the Marine Biotechnology and Biomedicine Center and co-lead author of the 39; study. "Now that we can relate these diagnostic chemical transformations to their enzymes and genes, we hope that researchers will be able to predict the toxicity potential of domoic acid in a harmful algal bloom to complement surveillance approaches." current. "
Researchers studying the monitoring and prediction of harmful algal blooms say that this discovery gives hope for a better understanding of the phenomenon and can help better project the trajectory of domoic acid events into the future. response to future climate change.
"This breakthrough marks an obvious point of change in our understanding of these events, as much of the uncertainty surrounding the toxic proliferations of Pseudo-nitzschia results from our incomplete understanding of the synthesis. of domoic acid, "said a biological oceanographer. Clarissa Anderson, director of the SCRSCS (Southern California Coastal Ocean Observing System), who did not participate in the study. "The Holy Grail of the prediction of harmful algal blooms on the west coast and elsewhere provides for when, where and, ultimately, why Pseudo-nitzschia activates or deactivates the production of domoic acid. -be never prevent this type of nuisance algae bloom, but we can better monitor the early stages of domoic acid production. "
The study, titled "Biosynthesis of domoic neuroid acid in a diatom-forming bloom," was in preparation for five years.
Explore more:
What causes the algal blooms to become toxic?
More information:
J.K. Brunson et al., "Biosynthesis of domoic acid neurotoxin in a diatom bloom" Science (2018). science.sciencemag.org/cgi/doi… 1126 / science.aau0382
G. Pohnert el al., "The manufacture of a plankton toxin" Science (2018). science.sciencemag.org/cgi/doi… 1126 / science.aau9067
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