title: Deletion of the transcriptional regulator cyAbrB2 deregulates primary carbon metabolism in Synechocystis sp. PCC 6803.
abstract: cyAbrB is a transcriptional regulator unique to and highly conserved among cyanobacterial species. A gene-disrupted mutant of cyabrB2 (sll0822) in Synechocystis sp. PCC 6803 exhibited severe growth inhibition and abnormal accumulation of glycogen granules within cells under photomixotrophic conditions. Within 6 h after the shift to photomixotrophic conditions, sodium bicarbonate-dependent oxygen evolution activity markedly declined in the ΔcyabrB2 mutant, but the decrease in methyl viologen-dependent electron transport activity was much smaller, indicating inhibition in carbon dioxide fixation. Decreases in the transcript levels of several genes related to sugar catabolism, carbon dioxide fixation, and nitrogen metabolism were also observed within 6 h. Metabolome analysis by capillary electrophoresis mass spectrometry revealed that several metabolites accumulated differently in the wild-type and mutant strains. For example, the amounts of pyruvate and 2-oxoglutarate (2OG) were significantly lower in the mutant than in the wild type, irrespective of trophic conditions. The growth rate of the ΔcyabrB2 mutant was restored to a level comparable to that under photoautotrophic conditions by addition of 2OG to the growth medium under photomixotrophic conditions. Activities of various metabolic processes, including carbon dioxide fixation, respiration, and nitrogen assimilation, seemed to be enhanced by 2OG addition. These observations suggest that cyAbrB2 is essential for the active transcription of genes related to carbon and nitrogen metabolism upon a shift to photomixotrophic conditions. Deletion of cyAbrB2 is likely to deregulate the partition of carbon between storage forms and soluble forms used for biosynthetic purposes. This disorder may cause inactivation of cellular metabolism, excess accumulation of reducing equivalents, and subsequent loss of viability under photomixotrophic conditions.
authors.affiliation: Graduate School of Science and Engineering , Saitama University, Saitama 338-8570, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kaniya
authors.forename: Ayumi
authors.initials: A
authors.lastname: Kizawa
authors.forename: Atsuko
authors.initials: A
authors.lastname: Miyagi
authors.forename: Maki
authors.initials: M
authors.lastname: Kawai-Yamada
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Uchimiya
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Kaneko
authors.forename: Yoshikata
authors.initials: Y
authors.lastname: Nishiyama
authors.forename: Yukako
authors.initials: Y
authors.lastname: Hihara
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D007656:Ketoglutaric Acids / Q000378:metabolism / Q000494:pharmacology; D055442:Metabolome; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics; D019289:Pyruvic Acid / Q000378:metabolism; D017693:Sodium Bicarbonate / Q000378:metabolism; D046939:Synechocystis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D007656:Ketoglutaric Acids; D002244:Carbon; D019289:Pyruvic Acid; D017693:Sodium Bicarbonate; D009584:Nitrogen