Interstrain variability in toxin production in populations of the cyanobacterium Microcystis aeruginosa from water-supply reservoirs of Andalusia and lagoons of Donana National Park (southern Spain)

Microcystis aeruginosa (Cyanobacteria) is known to be the main source of toxic blooms affecting humans and animals in inland water systems. Usually, this toxic species occurs in dense blooms with patches of high and low toxin concentrations at the same time. Environmental causes have usually been suggested to explain this heterogeneity, but genetic differences also play an important role. We measured variability in toxin production (toxin concentration and toxin quota) both within and between populations of M. aeruginosa. Twenty-six clonal cultures of M. aeruginosa, isolated from two water-supply reservoirs in Andalusia (southern Spain) and three lagoons from Donana National Park, were grown under the same environmental conditions and their toxin production was measured. Statistically significant variation in the production of microcystin was found both within and between populations, but was greater within than between populations. These results suggest that interstrain variability could be the main cause of observed spatial-temporal heterogeneity in toxin production. This raises uncertainty in water-supply management early-warning systems based on cell abundance.