Microbial photoproduction of heptane
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 O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=76 SRC="FIGDIR/small/603920v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@1dbfebforg.highwire.dtl.DTLVardef@31dbaforg.highwire.dtl.DTLVardef@14dfcd5org.highwire.dtl.DTLVardef@11234d4_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIAn E. coli strain producing heptane under blue light is described. C_LIO_LIExpression of FAP fused with TrxA increases heptane by 10-fold. C_LIO_LIA blue light-inducible promoter ensures high coexpression of FAP and thioesterase. C_LIO_LICuphea hookeriana thioesterase and Chlorella variabilis FAP give highest production C_LIO_LIHighest reported heptane productivity (22 mg.L-1.day-1) in 100 mL photobioreactors. C_LI