Toxic blooms have long plagued Lake Erie, but the origins of one of their most dangerous neurotoxins have remained elusive. A new genomic analysis now identifies the culprit: specific strains of the cyanobacterium Dolichospermum, which carry the genes needed to produce saxitoxin – a potent compound previously detected in the lake without a known biological source.
Scientists from the University of Michigan pieced together the full genome of the toxin-producing organism using shotgun sequencing, a technique that captures all DNA present in a water sample. By reconstructing the genome directly from bloom material, the team was able to pinpoint the gene cluster responsible for saxitoxin biosynthesis. Only some Dolichospermum strains contained this cluster, highlighting the genetic diversity hidden within a visually uniform bloom.
Environmental patterns added further clues. Warmer water samples often contained higher levels of the saxitoxin gene, while sites with elevated ammonium showed lower abundance. According to the study, this may relate to Dolichospermum’s ability to use dinitrogen gas – a trait visible in the genome and one that can provide a competitive advantage when fixed nitrogen is scarce. “One of the neat things about having the whole genome is you can see everything the organism can do, at least theoretically,” said corresponding author Gregory Dick in a press release. “You have the whole blueprint.”
The findings sharpen the picture of how harmful algal blooms evolve under shifting lake conditions. As Dick noted, “The main advantage of knowing which organism produces the toxin is that it helps us understand the conditions that cause toxin production.” With climate-driven warming altering biological communities each year, the team plans to track the abundance of toxin-producing strains more closely.
Newsletters
Receive the latest analytical science news, personalities, education, and career development – weekly to your inbox.
