Metabolomics-based analysis revealing the alteration of primary carbon metabolism by the genetic manipulation of a hydrogenase HoxH in Synechocystis sp. PCC 6803

Cyanobacterial hydrogenases are important owing to the association between hydrogen metabolism and cell physiology and the production of future renewable energy. Many studies have examined hydrogen productivity, transcriptional regulation of hydrogenases, and the biochemistry of hydrogenases; however the relationship between hydrogen and primary carbon metabolism using metabolomic techniques has not been elucidated. Here, we studied the effect of the genetic manipulation of a hydrogenase on primary carbon metabolism in the model unicellular cyanobacterium Synechocystis sp. PCC 6803. Metabolomic analysis revealed that the hoxH mutant with reduced hoxH transcripts exhibited increased sugar phosphates in dark, anaerobic conditions. Organic acids, lactate, succinate, fumarate, and malate increased substantially by the hoxH mutation both inside and outside of cells in dark, anaerobic conditions. Transcriptome analysis revealed higher expression of genes encoding the RNA polymerase sigma factor SigE, which is a positive regulator of sugar catabolism, and 6-phosphogluconate dehydrogenase in the hoxH mutant than in the wild-type strain. Immunoblotting results showed that sugar catabolic enzymes and SigE proteins increased in the hoxH mutant. These results demonstrate the wide alterations of primary metabolism by the genetic manipulation of a hydrogenase subunit in this cyanobacterium.