Genomic analysis of parallel-evolved cyanobacterium Synechocystis sp. PCC 6803 under acid stress. Synechocystis sp. PCC 6803

Experimental evolution is a powerful tool for clarifying phenotypic and genotypic changes responsible for adaptive evolution. In this study, we isolated acid-acclimated Synechocystis sp. PCC 6803 strains to identify genes involved in acid tolerance. Synechocystis 6803 are rarely found in habitants with pH < 5.75. The parent strain was cultured in BG-11 at pH 6.0. We gradually lowered the pH of the medium from pH 6.0 to pH 5.5 over 3 months. Our acclimated cells could grow in acid stress conditions at pH 5.5, whereas the parent cells could not. We performed whole-genome sequencing and compared the acid-acclimated and parent strains, thereby identifying 11 SNPs in the acid-acclimated strains. These results suggest that SNPs in certain genes are involved in acid stress tolerance in Synechocystis 6803.