Scientists at the University of Michigan have pinpointed Dolichospermum, a type of cyanobacteria, as the organism producing dangerous saxitoxins in Lake Erie's harmful algal blooms. Using genome sequencing, they found that only certain strains generate the potent neurotoxins, with warmer waters and low ammonium levels potentially favoring their growth. This discovery could improve monitoring and management of blooms amid climate change.
Lake Erie has long struggled with harmful algal blooms (HABs) during warm months, when cyanobacteria multiply rapidly and release toxins that threaten wildlife and human health. A 2014 bloom produced microcystin, endangering Toledo's drinking water supply, while saxitoxin—a powerful neurotoxin—was first detected in 2007, though its source remained elusive until now.
University of Michigan researchers, led by Paul Den Uyl, collected samples from HABs across the lake and employed 'shotgun' sequencing to analyze DNA. This technique allowed them to reconstruct genomes and identify genes responsible for saxitoxin production. Their findings, published in Environmental Science & Technology (2025, 59(15):7600, DOI: 10.1021/acs.est.4c10888), reveal that Dolichospermum strains are the culprits, but only specific ones carry the toxin-producing capability.
"The main advantage of knowing which organism produces the toxin is that it helps us understand the conditions that cause toxin production—that is, what conditions make those organisms successful," said Gregory Dick, professor of earth and environmental sciences and director of the Cooperative Institute for Great Lakes Research (CIGLR). The team noted higher abundance of the saxitoxin gene in warmer waters, raising concerns about climate-driven changes. "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?" Den Uyl added.
Dolichospermum's ability to fix nitrogen from atmospheric dinitrogen gas provides a competitive edge in low-ammonium environments, potentially exacerbating blooms. "One of the neat things about having the whole genome is you can see everything the organism can do, at least theoretically," Dick explained. The researchers have monitored saxitoxin for nine years but emphasize it's too early to predict long-term trends. Future efforts will track the organism's abundance to inform policy and management.