Rapid adaptation of harmful cyanobacteria to rising CO2

Cyanobacterial blooms pose a major threat to the water quality of many eutrophic lakes and reservoirs. Cyanobacteria are thought to be very effective competitors when CO2 levels are depleted during dense blooms. Their response to elevated CO2 is less understood, however. We study competition among cyanobacteria, and find both laboratory and field evidence for natural selection of strains with different carbon uptake systems at different CO2 levels. Our results demonstrate that changes in inorganic carbon availability act as an important selective factor in cyanobacterial communities and suggest that future harmful cyanobacterial blooms will have a genotype composition that differs from contemporary blooms and will be tuned to the high-CO2 conditions.