University of Michigan Researchers Identify Source of Harmful Toxins in Lake Erie Blooms
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A new study pinpoints Dolichospermum cyanobacteria as the primary producer of risky toxins-including saxitoxin and microcystin-threatening water quality and public health in Lake Erie.
During the warmer months, Lake Erie is susceptible to rapid growth of cyanobacteria, commonly known as blue-green algae. These blooms can release toxins at levels harmful to both wildlife and people. Now, researchers at the University of Michigan have made a critical breakthrough, identifying the specific organism responsible for producing these toxins: a type of cyanobacteria called Dolichospermum. This discovery is a major step forward in understanding, predicting, and mitigating the risks posed by harmful algal blooms (HABs).
The Threat of Lake Erie’s Toxic Blooms
Lake erie has faced recurring challenges wiht toxic algal blooms. A significant bloom in 2014 generated microcystin, a toxin that severely threatened Toledo’s drinking water supply. Even earlier, in 2007, scientists detected toxins in the lake, but the source remained elusive. Traditional methods of identifying the source of these toxins relied on culturing and identifying organisms,a process that is both time-consuming and often inaccurate,as many species are tough to grow in the lab.
Unlocking the Genetic Code
To overcome these limitations, the research team employed metagenomic sequencing, a method that analyzes all DNA present in a water sample. This allowed them to reconstruct the complete genome of the organisms present and then search for the genes responsible for producing saxitoxin.
Their analysis revealed multiple strains of Dolichospermum inhabiting Lake Erie. However,the ability to produce saxitoxin was not global across all strains. The reason for this variation remains unclear, prompting further investigation into the environmental factors influencing toxin production.
Environmental Factors Influencing Toxin Production
The research team collected samples from various locations across Lake Erie throughout the year, measuring the prevalence of the saxitoxin-related gene. They consistently found higher levels of this gene in warmer water.
“That is interesting as we do know that the lakes are changing with climate change,” noted a scientist at the University of Michigan’s Cooperative Institute for Great Lakes Research (CIGLR). “With the warming of the lakes, one of the big questions is, how is that going to change the biological communities, including harmful cyanobacterial blooms?”
Interestingly, the gene linked to saxitoxin was less common in areas with high levels of ammonium. Researchers suspect this is connected to Dolichospermum’s unique ability to utilize nitrogen in the form of dinitrogen, an abundant gas in the atmosphere. According to researchers, only a limited number of organisms can harness nitrogen in this way, giving Dolichospermum a competitive edge under certain conditions.
“One of the neat things about having the whole genome is you can see everything the organism can do, at least theoretically,” said the director of CIGLR. “You have the whole blueprint for what the organism can do, and we do see the capability of obtaining fixed nitrogen from the water.It’s just that getting it in the form of dinitrogen gas is kind of a superpower. Not a lot of organisms can do that, and it makes them more competitive under those conditions.”
Long-Term Monitoring and Future Research
The researchers have been monitoring saxitoxin levels in Lake Erie for nine years, but acknowledge that this timeframe is insufficient to definitively determine whether toxin levels will increase as the climate continues to warm.
“But now that we certainly know who’s producing it, I think we can keep a better watch on these organisms and we can also directly assess the gene abundance over time,” a researcher stated. “We plan to continue monitoring the abundance of this organism, but it’s too early to tell if it’s becoming more abundant. It’s just a correlation,but that correlation with temperature is concerning.”
Their findings, published in the journal Environmental Science & Technology, represent a significant advancement in our understanding of harmful algal blooms and their impact on freshwater ecosystems.Continued monitoring and research will be crucial to protecting Lake Erie and the communities that depend on it.
