Overexpression of glucose-6-phosphate isomerase in Synechocystis sp. PCC 6803 with disrupted glycogen synthesis pathway improves exopolysaccharides synthesis

Abstract

The exopolysaccharides (EPS) acting as an extracellular protective molecule in cyanobacteria have unique characteristics suitable for various applications. The synthesis of EPS which has a complex structure is regulated by the expression of multiple gene clusters. In order to increase the EPS production, it is essential to enhance the synthesis of fundamental sugar units. Thus, the glgC encoding glucose-1-phosphate adenylyltransferase involved in glycogen synthesis was disrupted to redirect most of the carbon sources including glucose into EPS synthesis pathway. On the other hand, the gpi encoding glucose-6-phosphate isomerase was overexpressed to enhance the sugar metabolism from photosynthetic carbon reduction cycle, which led to the accumulation of various sugar monomers. The glgC knockout strain containing gpi overexpression (▲gpi-∆glgC) produced the highest content of EPS accompanied by the increases in its composition of glucose, galactose, xylose, mannose, rhamnose, fucose and uronic acid. Furthermore, ▲gpi-∆glgC strain with the total EPS content of about 251 μg/108 cells was more tolerant to high light intensity as well as UV irradiance.