Abstract
Hexanoic acid and its derivatives have been recently recognized as value-added materials and can be synthesized by several microbes. Of them, Megasphaera elsdenii has been considered as an interesting hexanoic acid producer because of its capability to utilize a variety of carbons sources. However, the cellular metabolism and physiology of M. elsdenii still remain uncharacterized. Therefore, in order to better understand hexanoic acid synthetic metabolism in M. elsdenii, we newly reconstructed its genome-scale metabolic model, iME375, which accounts for 375 genes, 521 reactions, and 443 metabolites. A constraint-based analysis was then employed to evaluate cell growth under various conditions. Subsequently, a flux ratio analysis was conducted to understand the mechanism of bifurcated hexanoic acid synthetic pathways, including the typical fatty acid synthetic pathway via acetyl-CoA and the TCA cycle in a counterclockwise direction through succinate. The resultant metabolic states showed that the highest hexanoic acid production could be achieved when the balanced fractional contribution via acetyl-CoA and succinate in reductive TCA cycle was formed in various cell growth rates. The highest hexanoic acid production was maintained in the most perturbed flux ratio, as phosphoenolpyruvate carboxykinase (pck) enables the bifurcated pathway to form consistent fluxes. Finally, organic acid consuming simulations suggested that succinate can increase both biomass formation and hexanoic acid production.
Highlights
Hexanoic acid and its derivatives are generally used for the production of artificial flavors and food additives, as well as plastics, rubber, transportation fuel, and pharmaceuticals [1,2,3,4]
M. elsdenii has noticeable advantages, as it can consume diverse carbohydrates such as starch, mannitol, glucose, maltose, and sucrose, which are economic carbon sources [8], and achieve higher titre of hexanoic acid compared with other candidates, namely, 19 g/L and 28.42 g/L from glucose [9] and sucrose [1], respectively
As previous studies have reported that M. elsdenii is able to grow on all of these carbon sources, we added new transport reactions based on the information available from the KEGG and Biocyc databases
Summary
Hexanoic acid and its derivatives are generally used for the production of artificial flavors and food additives, as well as plastics, rubber, transportation fuel, and pharmaceuticals [1,2,3,4]. They are mainly produced via the multi-step chemical conversion of petroleum products and natural oils, recently, microbial cell factories have been considered as a promising approach for the sustained production of this straight six-carbon chain carboxylic acid. M. elsdenii has noticeable advantages, as it can consume diverse carbohydrates such as starch, mannitol, glucose, maltose, and sucrose, which are economic carbon sources [8], and achieve higher titre of hexanoic acid compared with other candidates, namely, 19 g/L and 28.42 g/L from glucose [9] and sucrose [1], respectively
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