The enzymes responsible for the production of one of the most toxic and fast-acting neurotoxins associated with freshwater harmful algal blooms in lakes and ponds were discovered and validated by scientists from Scripps Institution of Oceanography at the University of California San Diego, the University of São Paulo, and UC Santa Cruz.
The researchers used a combination of genetic and biochemical experiments to demonstrate how freshwater cyanobacteria manufacture the neurotoxin guanitoxin. This research indicated that cyanobacteria that produce guanitoxin are more common in the United States than previously thought, paving the way for novel molecular diagnostic testing to better inform and protect the public from this natural freshwater toxin.
Findings were described in a paper published in the Journal of the American Chemical Society on May 18, 2022.
According to research lead author Stella Lima, a former PhD student at the University of So Paulo and visiting scholar at Scripps Oceanography, the paper “shows guanitoxin being produced in freshwater bodies that have undergone past very toxic events.”
According to Timothy Fallon, a Scripps postdoctoral scientist in the laboratory of Scripps marine chemical biologist Bradley Moore, where Lima was a visiting scholar, guanitoxin is one of the most potent neurotoxins produced by cyanobacteria and has a mechanism of action similar to pesticides and chemical warfare agents.
When cyanobacteria, often known as blue-green algae, becomes prevalent in lakes and ponds, harmful algal blooms (HABs) occur. Different cyanotoxins are produced by these freshwater HABs, which can affect adjacent animals and people.
According to federal health officials, exposed people may have symptoms such as stomach pain, headache, vomiting, liver damage, or neurological impairment, depending on the cyanotoxin involved. Many places have declared emergencies and issued “do not drink” advice over the years.
We found these genes in lots of different fresh water sources, but nobody has looked for or monitored for this particular toxin environmentally.
Shaun McKinnie
Animal and pet deaths have also been reported after coming into touch with contaminated water. Freshwater HABs can pose a slew of social and economic issues for communities, as well as being a serious public health concern, according to Lima.
Certain cyanotoxins, such as microcystin, cylindrospermopsin, saxitoxin, and anatoxin-a, are tested and monitored because methods are available, but despite the fact that guanitoxin is the second most toxic cyanotoxin, “no one is looking for it” because the right detection and monitoring methods aren’t available, according to Lima.
Lima discovered a set of genes she suspected were responsible for the production of guanitoxin by a cyanobacterium isolated from a massive freshwater bloom in Brazil as a PhD student in 2016. Marli Fiore, Lima’s former PhD adviser and co-author of the study, isolated the strain from the Tapacurá reservoir in Pernambuco, Brazil, and has nurtured and grown it.
Lima sought a partnership to corroborate her suspicions after this revelation. So she went to UC San Diego in 2018 to study with Moore, who had pioneered the initial biochemical investigations on guanitoxin in the early 1990s. According to Lima, the team of experts collaborated to determine the specific activities of all nine enzymes involved in the conversion of an ordinary amino acid to a neurotoxic.
Researchers went through hundreds of samples from publicly available environmental data for the guanitoxin biosynthetic genes after uncovering the genes involved in the manufacture of guanitoxin and rigorously validating their functions.
According to Moore, who is a co-corresponding author of the study, the researchers were able to discover toxin genes for guanitoxin in environmental hotspots in inhabited areas in the United States.
The toxin genes for guanitoxin were consistently discovered in two places of concern: Lake Erie near Toledo, Ohio, and Lake Mendota, Wisconsin. The Amazon River in Brazil, the Columbia River in Oregon, and the Delaware River in Delaware are among the other regions where detection is possible.
“We found these genes in lots of different fresh water sources, but nobody has looked for or monitored for this particular toxin environmentally,” said Shaun McKinnie, a chemistry and biochemistry assistant professor at UC Santa Cruz and former postdoctoral scholar in the Moore Lab, who contributed to the study.
“Here’s this neurotoxic potential in these lakes that people use recreationally, but this toxin has gone under the radar until our work,” Fallon said.
Fieldwork to find other sites where guanitoxin may be created, according to Moore, should be part of the follow-up work.
Cyanobacterial blooms are growing more common in the United States and around the world, owing to climate change and the release of fertilizers and other agricultural chemicals into bodies of water.
HABs can be seen on the surface of freshwater lakes, but “cyanotoxins can be present before and after blooms are visible,” according to the federal Environmental Protection Agency (EPA). As a result, cyanotoxin levels should be established through laboratory testing of the water.
“Now that we figured out the guanitoxin pathway at the genomic level, we can also give additional pieces of information to say: ‘This is a safe body of water, or this is a less safe body of water; Does this have the ability to become toxic and can we predict toxic events?’” McKinnie said.
The researchers have filed a provisional patent application based on the concept of using the guanitoxin biosynthetic gene sequences they identified in the lab and applying molecular diagnostics using those sequences to find the genes in the environment.
In addition to Lima, Fallon, Moore, Fiore, and McKinnie, other study co-authors include Endrews Delbaje, Ernani Pinto and Felipe Dörr from the University of São Paulo; former Moore Lab scientist Hanna Luhavaya; current Scripps Oceanography PhD student Steffaney Wood; UC Santa Cruz researchers Jennifer Cordoza, Austin Hopiavuori, and Jackson Baumgartner; Jonathon Chekan from University of North Carolina Greensboro; Danillo Alvarenga from the University of Copenhagen; and Augusto Etchegaray from the Pontifical Catholic University of Campinas in Brazil.
The National Institute of Environmental Health Sciences, the Sao Paulo Research Foundation, and the National Council for Scientific and Technological Development all contributed to the study’s funding. Other sources of support included the Life Sciences Research Foundation’s Simons Foundation Fellowship, the Brazilian Federal Agency for the Support Evaluation of Graduate Education, startup funds, and a Faculty Research Grant from UC Santa Cruz.
