Effects of rising CO₂ on the harmful cyanobacterium Microcystis

The waters of our planet are full with cyanobacteria that use CO₂, water and light for photosynthesis. Cyanobacteria form the base of the food web and have a strong impact on all life on Earth.
Yet, not all cyanobacteria are beneficial. Harmful cyanobacteria (also known as ‘blue-green algae’) can form dense blooms in lakes and produce toxins, which leads to all sorts of problems. These blooms can threaten drinking water supplies, recreational activities, livestock, birds and human health.
Since the industrial revolution, atmospheric CO₂ concentrations are rising strongly. Cyanobacteria are generally assumed to be favored at low CO₂ conditions, because of the presence of an effective CO₂-concentrating mechanism (CCM) to fix CO₂. Yet, how will harmful cyanobacteria, such as the ubiquitous harmful cyanobacterium Microcystis aeruginosa, respond to rising CO₂? Are they well-adapted to deal with climate change? Will cyanobacterial blooms intensify? Will the genetic composition and toxicity of blooms change? And what can we do to combat these blooms?
The results in this thesis demonstrate how genetic diversity in the carbon uptake systems provide Microcystis and other cyanobacteria with the potential for rapid microevolutionary adaptation to changes in CO₂ conditions, with a selective advantage for strains with high-flux uptake systems at elevated CO₂ levels. Furthermore, the results indicate that rising atmospheric CO₂ concentrations are likely to increase the frequency and intensity of cyanobacterial blooms in eutrophic waters, and possibly also the toxicity of these blooms. These findings and more are discussed in this PhD thesis.