Butyric acid is commonly used in fragrance, pharmaceuticals, plastics, and more. In addition, it is also a precursor to butanol fuel. We have previously engineered a strain of cyanobacteria for butanol production. However, the productivity was limited by the product toxicity. Here, we evaluated the potential of butyrate production from CO2 using cyanobacteria as it is non-toxic. Here, we constructed two pathways leading to the synthesis of butyrate. The two pathways share the same core carbon chain elongation mechanism which converts acetyl-CoA to butyryl-CoA. Subsequently, we evaluated the effectiveness of ATP-generating pathway catalyzed by phosphotransbutyrylase and butyrate kinase and ATP-independent pathway catalyzed by thioesterase. Results indicate insignificant difference between the two pathways as identified highly active enzymes for removing CoA and liberating butyrate in both pathways. The resulting strains produced significant amount of butyrate close to 1 g/L, representing a three-fold higher titer than what has been demonstrated for photosynthetic butanol synthesis. Direct photosynthetic reduction of CO2 into butyrate is advantageous over traditional sugar-based fermentation as it can be directly used to convert CO2 waste stream from various industries into useable chemicals.

Photosynthetic production of butyrate: A versatile chemical and non-toxic alternative for butanol in cyanobacteria

253rd National Meeting (2017)

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