Abstract
Arthrospira (Spirulina) platensis is a promising feedstock and host strain for bioproduction because of its high accumulation of glycogen and superior characteristics for industrial production. Metabolic simulation using a genome-scale metabolic model and flux balance analysis is a powerful method that can be used to design metabolic engineering strategies for the improvement of target molecule production. In this study, we constructed a genome-scale metabolic model of A. platensis NIES-39 including 746 metabolic reactions and 673 metabolites, and developed novel strategies to improve the production of valuable metabolites, such as glycogen and ethanol. The simulation results obtained using the metabolic model showed high consistency with experimental results for growth rates under several trophic conditions and growth capabilities on various organic substrates. The metabolic model was further applied to design a metabolic network to improve the autotrophic production of glycogen and ethanol. Decreased flux of reactions related to the TCA cycle and phosphoenolpyruvate reaction were found to improve glycogen production. Furthermore, in silico knockout simulation indicated that deletion of genes related to the respiratory chain, such as NAD(P)H dehydrogenase and cytochrome-c oxidase, could enhance ethanol production by using ammonium as a nitrogen source.
Highlights
In recent years, bioproduction of fuels and chemicals from biomass has been intensively investigated to achieve a sustainable society
A genome-scale metabolic model of A. platensis NIES-39 was constructed based on information from genome sequences, databases such as Kyoto Encyclopedia of Genes and Genomes (KEGG) [31] and CyanoBase [30], and previously published material
Cyanobacteria have been reported to possess an incomplete TCA cycle because of a lack of α-ketoglutarate dehydrogenase, which converts α-ketoglutarate to succinyl-CoA [40, 41], and α-ketoglutarate dehydrogenase has not been identified in A. platensis NIES-39
Summary
Bioproduction of fuels and chemicals from biomass has been intensively investigated to achieve a sustainable society. Arthrospira (Spirulina) platensis, a filamentous non-N2-fixing cyanobacterium, is promising for use as a biomass feedstock because of its capability to accumulate a large amount of glycogen, which is an excellent feedstock for biofuel production [8, 9]. A. platensis has been produced as a superior nutrient because of its high content of protein and carotenes [11], and it is the most industrially cultivated microalgal species [12]. Its superior characteristics such as high pH tolerance and high salt tolerance [11] could prevent contamination by other organisms in outdoor cultivation
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