Abstract
Metabolic engineering of photosynthetic organisms is required for utilization of light energy and reducing carbon emission. We previously showed that a group 2 sigma factor SigE of Synechocystis sp. PCC 6803 globally activates transcription of sugar catabolic genes. In this study, we generated the strain overexpressing SigE and microarray analysis revealed that genes for the oxidative pentose phosphate pathway and glycogen catabolism increased in this strain. Immunoblotting revealed that protein levels of sugar catabolic enzymes such as glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glycogen phosphorylase, and isoamylase increased and the level of glycogen decreased in the SigE-overexpressing strain under light growth conditions. CE/MS analysis unraveled that metabolites of the TCA cycle and acetyl-CoA are altered by SigE overexpression. We also found that SigE-overexpressing strain exhibits defective growth under mixotrophic or dark conditions. We thus demonstrate that SigE overexpression activates sugar catabolism at transcript to phenotype levels, opening a sigma factor-based engineering for the modification of carbon metabolism in photosynthetic organisms.
