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Title: Deciphering cyanobacterial phenotypes for fast photoautotrophic growth via isotopically nonstationary metabolic flux analysis

item ABERNATHY, MARY - Washington University
item YU, JINGIE - Washington University
item MA, FANGFANG - Danforth Plant Science Center
item LIBERTON, MICHELLE - Washington University
item UNGERER, JUSTIN - Washington University
item HOLLINSHEAD, WHITNEY - Washington University
item GOPALAKRISHNAN, SARATRAM - Pennsylvania State University
item HE, LIAN - Washington University
item MARANAS, COSTAS - Pennsylvania State University
item PAKRASI, HIMADRI - Washington University
item Allen, Douglas - Doug
item TANG, YINJIE - Washington University

Submitted to: Biotechnology for Biofuels and Bioproducts
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2017
Publication Date: 11/16/2017
Citation: Abernathy, M.H., Yu, J., Ma, F., Liberton, M., Ungerer, J., Hollinshead, W., Gopalakrishnan, S., He, L., Maranas, C.D., Pakrasi, H., Allen, D.K., Tang, Y. 2017. Deciphering cyanobacterial phenotypes for fast photoautotrophic growth via isotopically nonstationary metabolic flux analysis. Biotechnology for Biofuels. 10:273.

Interpretive Summary: Photosynthetic systems are the primary means by which carbon, taken from the air as carbon dioxide, is converted in to organic forms to make food, feed and fuel. Therefore a better understanding of how carbon is used for growth and the production of biomass is important for food security as well as biotechnological purposes. In this study a simple model system that has the fastest growth rate of any known cyanobacteria was studied under several growth conditions that included varied availability to light. We established bioreactor conditions that were optimal relative to batch culturing and resulted in the minimal loss of carbon dioxide from respiration and CO2 releasing metabolic steps. As a result the use of carbon was more efficient and provided a unique description of optimal growth relative to other photosynthetic systems. The findings are important because enhanced growth and biomass production as a result of efficient photosynthesis will be increasingly important for production of renewable sources of energy and chemical feed stocks as the world population continues to grow and non-renewable resources become more limited.

Technical Abstract: Synechococcus elongatus UTEX 2973 is the fastest growing cyanobacterium that has been reported, demonstrating significant potential for photobiorefinery applications due to its high biomass yields and production rates. To understand its phenotypical properties, isotopically nonstationary metabolic flux analysis (INST-MFA) was employed with photobioreactors (doubling time ~2 hours) via 13C-pulse, LC-MS analysis of labeling dynamics of central metabolites, and Isotopomer Network Compartmental Analysis (INCA). Compared to other cyanobacteria strains, Synechococcus 2973 flux to pyruvate comes primarily from pyruvate kinase and less from malic enzyme. Minimal flux through the oxidative pentose phosphate pathway was also observed (OPPP; further confirmed by the normal growth of 'zwf mutant). These features minimize CO2 loss from the central metabolism and reveal highly efficient carbon utilization. Furthermore, metabolite concentrations, measured by mass isotopomer ratio analysis, indicated higher sugar phosphate levels in Synechococcus 2973, but 5~10 fold lower concentrations of acetyl-CoA and TCA cycle acids (relative to a heterotroph, E. coli). Compared to photobioreactor cultures, cyanobacteria in shake flasks had decreased fluxes but accumulated greater central metabolites and glycogen and a decrease in anabolic rates during light-limiting conditions. This study elucidates the fast-growth phenotype of Synechococcus 2973 and describes the redirection of carbon flowto increase production of desirable end products.