ANN ARBOR—Cyanobacteria blooms in places like Lake Erie can persist for months, long after most of the available nutrients in the water have been depleted. How do these troublesome photosynthetic organisms, sometimes called blue-green algae, manage it?

In a study published online July 25 in the journal Molecular Ecology, University of Michigan biologists and their colleagues report that different strains of the common cyanobacterium Microcystis aeruginosa appear to be adapted to different levels of the nutrient phosphorus in the water.

As phosphorus is gradually depleted by high-nutrient-adapted cyanobacterial strains over the course of the summer, low-nutrient-adapted strains present in the same lake apparently take over.

“Interestingly, this low-nutrient-adapted genotype can be found in high-nutrient lakes as well, where it can likely thrive once high-nutrient-adapted Microcystis has depleted available nutrients,” said Vincent Denef, an assistant professor in the U-M Department of Ecology and Evolutionary Biology.

The first author of the paper is EEB research fellow Sara Jackrel.

“This can help explain why these blooms can persist for so long even after free nutrients are depleted,” Jackrel said.

M. aeruginosa is the toxin-producing cyanobacterium blamed for the 2014 Toledo water crisis.

The researchers did a genetic analysis of 46 M. aeruginosa isolates and their microbiomes, collected by collaborators at Michigan State University (Jeffrey White and Orlando Sarnelle), from 14 inland Michigan lakes with a wide range of phosphorus levels.

Along the nutrient gradient, they found differences in Microcystis genome structure and function, in how the organisms form the multicellular colonies that make them so successful in the environment, and in the microbiomes that help them grow.

More information:

• Study: Genome Evolution and Host Microbiome Shifts Correspond with Intraspecific Niche Divergence within Harmful Algal Bloom-Forming Microcystis aeruginosa