Salinity is increasing in many inland waters, on a world-wide scale, due to agricultural practices, droughts, or rise in sea level. In order to understand the effects of increased salinity on freshwater ecosystems, the cosmopolitan toxic cyanobacterium Microcystis aeruginosa (Kützing) Kützing was selected as a model. It is known that this species that this species cannot proliferate in salinity >10-15 g∙L-1 but the limit of the adaptation to salinity remains to be investigated.
To detect the maximum genetic adaptation capacity of three strains of M. aeruginosa (isolated from a freshwater reservoir with salinity <0.025 g∙L-1, i.e. without previous “evolution salinity history”) to the exposure of increased salinity.
An experimental evolutionary approach (ratchet experiment) was used. In order to analyze the differential evolutionary potential of three M. aeruginosa strains, two ratchet experiments were performed based on “soft” or “intense” exponentially increased salinity.
Acclimation (supported by the gene expression already present in the ancestral populations) was similar in the three strains in both ratchets experiments (“soft” and “intense”). A significant enhancement in resistance, supported by the selection of new genetic variants arising by mutations (genetic adaptation), was achieved in all derived populations in both ratchet experiments, and in the three strains. However, the results showed that the dynamics and the limit of genetic adaptation depend on previous adaptation history (historical contingency).