Acyl CoA reductases useful for bioproduction of hydrocarbons

Background Hydrocarbon-based biofuels—so-called drop-in fuels—have gained attention as sustainable alternatives to petroleum-derived fuels, yet their biological production remains limited by the availability of efficient enzymatic pathways for generating hydrocarbon precursors. Medium-chain alkanes produced by microorganisms represent a promising target, but the aldehyde-producing capabilities of acyl-CoA reductases (ACRs) from bacteria, plants, and animals have not been systematically compared. Because ACRs generate fatty aldehydes—key intermediates in hydrocarbon biosynthesis—understanding their diversity is essential for expanding biological fuel production strategies. In this study, we performed a comprehensive screening of ACRs across diverse organisms to identify enzymes with promising aldehyde-producing activity and to advance the development of a new microbial hydrocarbon biosynthesis pathway. Results Sixteen acyl-CoA reductases (ACRs) from microorganisms, plants, and animals were cloned and expressed in Escherichia coli and evaluated by coexpressing each enzyme with a cyanobacterial aldehyde decarbonylase to enable hydrocarbon formation. Several Arabidopsis thaliana ACRs produced higher alkane levels than microbial and animal enzymes. To further examine plant-derived enzymes, ACR homologs with high amino acid similarity to A. thaliana ACR1 and ACR2 were cloned from multiple plant species and tested. Among these, ACR2 from Glycine max exhibited the highest alkane and alkene productivity, demonstrating that certain plant ACRs—known to generate long-chain alcohols—can also act on medium-chain fatty acids. Phylogenetic analysis of fourteen productive plant ACRs showed that ACRs similar to GmACR2 generated higher levels of C13 alkanes, although no clear trend was observed for C15 alkanes or C17 alkenes. Coexpression of GmACR2 with an aldehyde dehydrogenase from Schizosaccharomyces pombe enabled E. coli to produce C17 alkene from sugars. This demonstrates a previously unreported ACR–ALDH-based hydrocarbon biosynthesis pathway and expands the known enzymatic routes available for microbial hydrocarbon production. Conclusion This study identifies multiple microbial and plant-derived ACRs, particularly GmACR2, as effective catalysts for medium-chain hydrocarbon biosynthesis. Coexpression of GmACR2 with S. pombe aldehyde dehydrogenase shows that ACR–ALDH coexpression can enable microbial alkane and alkene production, which represents a previously unreported microbial hydrocarbon biosynthesis route. Because ACR and ALDH homologs are widely distributed across microorganisms, plants, and animals, these findings suggest that ACR–ALDH-based reductive processes may have contributed to the biogenic origin of petroleum, providing broader insight into both biofuel development and natural hydrocarbon formation.