The Effects of Dark Incubation on Cellular Metabolism of the Wild Type Cyanobacterium Synechocystis sp. PCC 6803 and a Mutant Lacking the Transcriptional Regulator cyAbrB2.

Masamitsu Hanai,Atsuko Miyagi,Kyoko Tanaka,Yusuke Sato,Yasuko Kaneko,Yukako Hihara,Yoshitaka Nishiyama,Maki Kawai-Yamada

doi:10.3390/life4040770

Masamitsu Hanai, Atsuko Miyagi + Show 6 more

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https://doi.org/10.3390/life4040770

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The cyAbrB2 transcriptional regulator is essential for active sugar catabolism in Synechocystis sp. PCC 6803 grown under light conditions. In the light-grown cyabrB2-disrupted mutant, glycogen granules and sugar phosphates corresponding to early steps in the glycolytic pathway accumulated to higher levels than those in the wild-type (WT) strain, whereas the amounts of 3-phosphoglycerate, phosphoenolpyruvate and ribulose 1,5-bisphosphate were significantly lower. We further determined that accumulated glycogen granules in the mutant could be actively catabolized under dark conditions. Differences in metabolite levels between WT and the mutant became less substantial during dark incubation due to a general quantitative decrease in metabolite levels. Notable exceptions, however, were increases in 2-oxoglutarate, histidine, ornithine and citrulline in the WT but not in the mutant. The amounts of cyAbrBs were highly responsive to the availability of light both in transcript and protein levels. When grown under light-dark cycle conditions, diurnal oscillatory pattern of glycogen content of the mutant was lost after the second dark period. These observations indicate that cyAbrB2 is dispensable for activation of sugar catabolism under dark conditions but involved in the proper switching between day and night metabolisms.

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Cyanobacteria are highly versatile organisms that modulate their metabolic activity in response to the availability of light and carbon [1,2,3]
The results indicate that cyAbrB2 makes less significant contribution to metabolite levels during dark incubation, the metabolic phenotypes of the ∆cyabrB2 mutant under light conditions were more notable in this study than in our previous report [10]
We examined the role of cyAbrB2 in cellular metabolic regulation under dark conditions by characterizing WT and the cyabrB2-disrupted mutant cells, using a metabolomic approach

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Introduction

Cyanobacteria are highly versatile organisms that modulate their metabolic activity in response to the availability of light and carbon [1,2,3]. The resulting sugars are catabolized via the oxidative pentose phosphate (OPP) pathway, the glycolytic pathway and the tricarboxylic acid (TCA) cycle to produce ATP, NAD(P)H and carbon compounds required for survival during the dark period. Since cyanobacteria have no organelles, most of abovementioned CO2 fixation, sugar catabolic and anabolic pathways are located in cytoplasm and several enzymes are shared among these metabolic reactions [4]. Coordination of these metabolic pathways is a prerequisite for optimal cyanobacterial growth under changing nutrient conditions

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