Carbohydrate metabolism in mutants of the cyanobacterium Synechocystis sp. PCC 6803 defective in glycogen and sucrose

GIARROCCO, L.E.; SALERNO, G.L.

Rosario

Congreso; VIII Congreso Argentino de Microbiología General, Rosario; 2013

SAMIGE

Glycogen and compatible solutes are the major polymeric and soluble carbohydrates in cyanobacteria and function as energy reserves and osmoprotectants, respectively. Glycogen biosynthesis is tightly regulated in response to different environmental cues. For instance, it has been reported that nitrogen limitation leads to glycogen accumulation in cyanobacteria, while photosynthesis is down-regulated, and the antenna system and accessory pigments are depleted. The genome of Synechocystissp. PCC 6803 encodes two glycogen synthase homologs, a bacterial-type glycogen synthase (GlgA-I) and an additional (starch-type) glycogen synthase referred as GlgA-II. Only one sucrose-phosphate synthase was found in Synechocystis PCC6803. In this study, the role of glycogen and sucrose in carbon metabolism in Synechocystisis analyzed via a comparative physiological and metabolic characterization of knockout mutants defective in glycogen and sucrosesynthesis. Synechocystisglycogen synthase and sucrose-phosphate synthase null mutants and double mutants were constructed. Growth rate and the intracellular content of glycogen and sucrose were compared between wild type (WT) and the mutant strains under standard, saline, photomixotrophic and nitrogen-limiting growth conditions. Single knockout mutants of glycogen synthases, ΔglgA-I and ΔglgA-II, respectively, were still able to accumulate similar amounts of glycogen as the wild-type indicating that the products of the glgA-I and glgA-II genes are partly redundant. This study shows that the analysis of deficiencies in glycogen and sucrose metabolism is a valuable tool for identification of metabolic regulatory principles and signals.