Increased polyhydroxybutyrate levels by ntcA overexpression in Synechocystis sp. PCC 6803

Synechocystis sp. PCC 6803, a unicellular cyanobacterial species, changes intracellular nitrogen and carbon metabolism through the transcription factor NtcA in response to nitrogen deficiency. In this study, the change in metabolites in carbon storages and the related metabolites after nitrogen depletion was analysed using ntcA-overexpressing strain. Levels of polyhydroxybutyrate (PHB), a biodegradable polyester, increased in the ntcA-overexpressing strain after nitrogen depletion. Capillary electrophoresis-mass spectrometry (CE-MS) analysis revealed that the levels of fumarate and malate increased and phosphoenolpyruvate, isocitrate, 2-oxoglutarate, succinate, phosphorylated monosaccharides and dihydroxyacetone phosphate decreased by ntcA overexpression. Respiratory activity decreased by ntcA overexpression, possibly resulted from the alteration of carbon metabolism and perturbation of redox balance. These results have revealed that NtcA is involved in the re-distribution of intracellular carbon sources to PHB and organic acids in the tricarboxylic acid cycle in this cyanobacterium.