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

Author
item HENDRY, JOHN - Indian Institute Of Technology
item PRASANNAN, CHARULATA - Indian Institute Of Technology
item MA, FANGFANG - Danforth Plant Science Center
item MOLLERS, BENEDIKT - University Of Copenhagen
item JAISWAL, DAMINI - Indian Institute Of Technology
item DIGMURTI, MADHURI - Indian Institute Of Technology
item Allen, Douglas - Doug
item FRIGAARD, NIELS-ULRIK - University Of Copenhagen
item DASGUPTA, SANTANU - Indian Institute Of Technology
item WANGIKAR, PRAMOD - Indian Institute Of Technology

Submitted to: Biotechnology and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2017
Publication Date: 6/29/2017
Publication URL: https://handle.nal.usda.gov/10113/5763063
Citation: Hendry, J.I., Prasannan, C., Ma, F., Mollers, B., Jaiswal, D., Digmurti, M., Allen, D.K., Frigaard, N., Dasgupta, S., Wangikar, P.P. 2017. Rerouting of carbon flux in a glycogen mutant of cyanobacteria assessed via isotopically non-stationary 13C metabolic flux analysis. Biotechnology and Bioengineering. 114(10):2298-2308. doi: 10.1002/bit.26350.

Interpretive Summary: Photosynthesis is an important metabolic process whereby the energy of sunlight is used to convert carbon dioxide from the air into organic compounds that are necessary to make food, feed and fuel. Therefore a quantitative understanding of this process is important for biotechnological applications and food security. In this study, genetic manipulations of a cyanobacteria (a single-celled organism that uses photosynthesis to generate food) resulted in altered photosynthetic metabolism. These alterations resulted in a change in biomass production and organic composition that were analyzed using isotopes (tracking molecules) and mathematical models. The experiments and models indicated that sugars were routed differently through metabolism to accommodate the observed alterations in the cyanobacteria. The findings suggested that there are possible opportunities to improve productivity in photosynthetic systems. The findings are important because strategies that enhance photosynthesis to produce more biomass will provide more food and renewable resources for the growing world population.

Technical Abstract: 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.