Toward Understanding the Ecophysiology of Freshwater and Marine Cyanobacteria under Different Salinities

The mechanism by which cyanobacteria have adapted fromlow to highsalinity and ultimately diversified in marine environments remainspoorly understood. To understand how freshwater and marine cyanobacteriarespond to high salinity, we selected a marine cyanobacteria, Synechococcus sp. PCC7002, and freshwater cyanobacteria, Synechococcus elongatus PCC7942. Photosynthetic growth ofPCC7002 and PCC7942 were enhanced and inhibited by the high salinity,respectively, which were also supported by the quantification of reducingequivalents and ATP in these two species. Growth under the high salinityreduced the photosynthetic activities for PCC7942, resulting in moreoxidative stress, which was opposite of the effect of high salinityon PCC7002. Transcriptomic analysis demonstrated that those key genesinvolved in synthetic and energy metabolisms as well as certain processesfor salinity acclimation and salinity signal transduction were significantlydownregulated in PCC7942 and upregulated in PCC7002 under the highsalinity, suggesting a potential functional regulatory mechanism fromperception, transduction, and acclimation of cyanobacteria to highsalinities. The findings of this study improve the understanding ofcyanobacterial ecophysiology under different salinities and shed lighton the evolutionary acclimation of cyanobacteria from freshwater tomarine environments. Phenotypicand transcriptomic analysis for the physiologicalresponses of freshwater and marine cyanobacteria under different salinities.