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The ideal fuel would be compatible with modern engines and infrastructure, and also be able to be produced in a renewable manner. No current biofuel has the same identical enough to that of diesel to be able to fully integrate with current engines and infrastructure. No known alternative fuel is able to match the chemical properties of diesel. Currently, the only way to renewably produce a fuel with the chemical properties and compatibility of diesel would be to make a biofuel with a composition identical to that of diesel. This would require a biological pathway that is able to produce alkanes, the main class of compounds in diesel. Alkanes are simple chains of carbon and hydrogen. The majority of the alkanes found in diesel have a carbon chain of 10 to 20 carbons long. Alkanes make up approximately 62% of jet diesel (a fairly representative diesel fuel)([[#References | [7]]]). This 62% includes 34% straight chain alkanes that contain only one linear chain, and 28% branched chain alkanes that contain 1 or more carbon branches. The remaining 38% consists mostly of cyclic and aromatic hydrocarbons. If long (10+) chain length alkanes could be biologically produced, it would allow for the production of a fuel that is both renewable and fully compatible with current engines and infrastructure.
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= The Solution: a Microbial Alkane Production Pathway=
[[Image:Washington2011_AlkaneAndBackCycle.png|right|400px|frameless]]
A recent study([[#References | [8]]]) conducted by LS9, inc. has shown the production of long chain length alkanes in ''E. coli'' using two genes found in many cyanobacteria species. The first gene codes for Acyl-ACP Reductase (AAR) which reduces long chain length acyl-ACPs into the corresponding fatty aldehydes. Acyl-ACPs are essential intermediates in fatty acid biosynthesis in every known organism, meaning that this system can work in a wide range of organisms. This long chain fatty acid acts as a substrate for Aldehyde Decarbonylase (ADC), the enzyme that removes the carbonyl group (C=O) from the fatty aldehyde, yielding an alkane one carbon shorter than the original Acyl-ACP and a molecule of formate. Since the vast majority of the fatty acyl-ACPs produced by ''E. coli'' have an even chain length, this system produces detectable amounts of only odd chain length alkanes. This study reported production of the C13, C15, and C17 alkanes, as well as the C17 alkene (unsaturated hydrocarbon), with a maximum alkane yield of 300 mg/L. This chain length range fall well within the range of those found in diesel, so this system is theoretically able to make the alkane portion of a fuel compatible with current engines and infrastructure.
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