Abstract
Cyanobacteria are an important group of photoautotrophic organisms that can synthesize valuable bio-products by harnessing solar energy. They are endowed with high photosynthetic efficiencies and diverse metabolic capabilities that confer the ability to convert solar energy into a variety of biofuels and their precursors. However, less well studied are the similarities and differences in metabolism of different species of cyanobacteria as they pertain to their suitability as microbial production chassis. Here we assemble, update and compare genome-scale models (iCyt773 and iSyn731) for two phylogenetically related cyanobacterial species, namely Cyanothece sp. ATCC 51142 and Synechocystis sp. PCC 6803. All reactions are elementally and charge balanced and localized into four different intracellular compartments (i.e., periplasm, cytosol, carboxysome and thylakoid lumen) and biomass descriptions are derived based on experimental measurements. Newly added reactions absent in earlier models (266 and 322, respectively) span most metabolic pathways with an emphasis on lipid biosynthesis. All thermodynamically infeasible loops are identified and eliminated from both models. Comparisons of model predictions against gene essentiality data reveal a specificity of 0.94 (94/100) and a sensitivity of 1 (19/19) for the Synechocystis iSyn731 model. The diurnal rhythm of Cyanothece 51142 metabolism is modeled by constructing separate (light/dark) biomass equations and introducing regulatory restrictions over light and dark phases. Specific metabolic pathway differences between the two cyanobacteria alluding to different bio-production potentials are reflected in both models.
Highlights
Cyanobacteria represent a widespread group of photosynthetic prokaryotes [1]
Macromolecules present in both cyanobacteria such as protein, carbohydrates, lipids, DNA, RNA, pigments, soluble pool and inorganic ions were assigned to their corresponding metabolic precursors (e.g., L-glycine, glucose, 16C-lipid, ATP, dGTP, betacarotene, coenzyme A and potassium respectively)
Experimental measurements showed that biomass composition varies for Cyanothece 51142 between light and dark conditions and nitrogen supplementation. Since pigments such as chlorophyll, carotenoids and phycocyanobilin play important roles in photosynthetic processes their quantities are higher under light conditions
Summary
Cyanobacteria represent a widespread group of photosynthetic prokaryotes [1]. By contributing oxygen to the atmosphere, they played an important role in the precambrian phase [2]. Cyanobacteria are primary producers in aquatic environments and contribute significantly to biological carbon sequestration, O2 production and the nitrogen cycle [3,4,5]. Their inherent photosynthetic capability and ease in genetic modifications are two significant advantages over other microbes in the industrial production of valuable bioproducts [6]. The short life cycle and transformability of cyanobacteria combined with a detailed understanding of their biochemical pathways are significant advantages of cyanobacteria as efficient platforms for harvesting solar energy and producing bio-products such as short chain alcohols, hydrogen and alkanes [6]
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