Microbial photoproduction of heptane
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Fatty Acid Photodecarboxylase (FAP) has emerged as a promising catalyst for the biological production of long-chain hydrocarbons. We have recently shown that purified FAP or FAP-expressing bacteria can efficiently convert octanoic acid into heptane, thus extending the potential applications of FAP to medium-chain hydrocarbons (i.e., solvent- or kerosene-type). The scarcity of natural sources of octanoic acid presents a challenge however. Here, we explore the heptane production capacity of a FAP-expressing E. coli strain engineered to biosynthesize octanoic acid via a specific thioesterase. Various FAPs and C8-specific thioesterases were tested. A blue-light-inducible promoter was used to avoid chemical inducers. We found that the expression of FAP fused with TrxA resulted in a 10-fold increase in heptane production. Coexpression of Cuphea hookeriana thioesterase and Chlorella variabilis FAP achieved the highest heptane titer (12.5 mg.L -1 ). Scale-up experiments in 100 mL photobioreactors allowed a constant production of heptane over two days (22 mg.L -1 .day -1 ).
Graphical Abstract
Highlights
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An E. coli strain producing heptane under blue light is described.
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Expression of FAP fused with TrxA increases heptane by 10-fold.
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A blue light-inducible promoter ensures high coexpression of FAP and thioesterase.
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Cuphea hookeriana thioesterase and Chlorella variabilis FAP give highest production
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Highest reported heptane productivity (22 mg.L -1 .day -1 ) in 100 mL photobioreactors.
