Synechocystis sp. PCC6803 glgA and glgAx mutant strains sequencing

In cyanobacteria, glycogen is the primary carbon storage polysaccharide. It is synthesized via the canonical GlgC-GlgA pathway, which involves the enzymes ADP-glucose pyrophosphorylase (AGP) and glycogen synthase (GlgA). The Synechocystis sp. PCC 6803 mutant lacking glycogen synthases (glgA) is not viable due to toxic accumulation of ADP-glucose, but can survive under saline conditions by redirecting this precursor to the synthesis of the osmolyte glucosylglycerol (GG). To investigate the synthesis pathway of this glycogen-like polysaccharide in the glgA strain, we tried to isolate spontaneous suppressor mutants capable of growth under non-permissive conditions (NaCl-free medium). Selection was performed by plating the glgA strain onto multiple NaCl-free BG11C plates. A single colony emerged, which was isolated and named glgAx. This suppressor strain could grow in BG11C irrespective of NaCl supplementation.