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Rerouting of carbon flux in a glycogen mutant of cyanobacteria assessed via isotopically non-stationary 13C metabolic flux analysis

Hendry, John I., Prasannan, Charulata, Ma, Fangfang, Möllers, K. Benedikt, Jaiswal, Damini, Digmurti, Madhuri, Allen, Doug K., Frigaard, Niels-Ulrik, Dasgupta, Santanu, Wangikar, Pramod P.
Biotechnology and Bioengineering 2017 pp. -11
Synechococcus, amino acids, biofuels, biotechnology, carbon, genetic engineering, glucose 1-phosphate, glucose-1-phosphate adenylyltransferase, glycogen, glycogen (starch) synthase, metabolic engineering, metabolic flux analysis, models, mutants, photosynthesis, photosynthetic bacteria, sucrose
Cyanobacteria, which constitute a quantitatively dominant phylum, are well known for their ability to carry out oxygenic photosynthesis. This prokaryotic group has attracted attention in biofuel applications due to favourable physiological characteristics, photosynthetic efficiency and amenability to genetic manipulations. However, quantitative aspects of cyanobacterial metabolism have received limited attention. In the present study, we have performed isotopic non-stationary 13C metabolic flux analysis (INST-13CMFA) to analyze rerouting of carbon in a glycogen deficient (glgA1/glgA2) mutant of the model cyanobacterium Synechococcus sp. PCC 7002. During balanced photoautotrophic growth, 10-20% of the fixed carbon is stored in the form of glycogen via a glycogen synthesis pathway that is conserved across the cyanobacterial phylum. Our results show that the glycogen synthase knockout orchestrates cascading effects on carbon partitioning for sugar storage. The immediate upstream reaction catalysed by ADP-glucose pyrophosphorylase is reduced and carbon is alternatively shuttled to make glucosylglycerol and sucrose. The alternative storage forms cannot fully account for the loss of glycogen with the remainder be allocated to organic acid formation presumably to provide carbon skeletons for amino acids. These results indicate flexibility at the glucose-1-phosphate (G1P) and ADP-glucose (ADPG) branch points and were qualitatively confirmed by Flux Balance Analysis and Minimization of Metabolic Adjustment (MOMA); however the quantitative amount of storage sugar reallocation varied between the flux analyses. The results are significant to metabolic engineering efforts with cyanobacteria where fixed carbon needs to be re-routed to products of interest.
  Data from: Rerouting of carbon flux in a glycogen mutant of cyanobacteria assessed via isotopically non‐stationary 13C metabolic flux analysis