Fuel, Vol.215, 123-141, 2018
Fungal metabolites as precursors to renewable transportation fuels
Fungi are known to produce hundreds of different polyketide, terpene, and terpenoid compounds and based on their chemical structures, 33 of these were selected for further assessment to identify compounds with potential for liquid transportation fuels. Eight of the 33 compounds were identified as having potential as gasoline blend components. Based on predicted boiling points and octane numbers, 2-ethyl-5,5-dimethyl-1,3-cyclopentadiene, sabinene, isobutyric acid, 1,8-cineole and linalool met the boiling point and octane number requirements used for the assessment, while 2-ethyl-5,5-dimethyl-1,3-cyclopentadiene and isobutyric acid would require some upgrading. Limonene, isoamyl acetate, and 2,2,5,5-tetramethyl-3-hexanone also have gasoline blend potential without upgrading. For diesel fuel, only 3,3,5-trimethyldecane met the boiling point, cetane number, and flashpoint requirements used for the assessment; however, with upgrading, 18 of the 33 compounds evaluated could potentially serve as blend components of diesel fuel. None of the 33 compounds without upgrading met the four ASTM D1655 specifications for Jet A and Jet A-1 fuel, but 3,3,5-trimethyldecane and limonene were very close. With chemical upgrading, 22 of the 33 compounds could have potential as jet fuel blend components. The monoterpene limonene and six sesquiterpenes were identified as fungal-derived compounds that with upgrading potentially could serve as components of high-energy jet, missile, or diesel fuels. The increasing availability of fungal genomes and transcriptomes enables the identification of important metabolic pathways for hydrocarbon production. The number of fungal-based compounds having potential for use in hydrocarbon fuels and products is increasing as new compound and pathway discoveries are made and advances in metabolic engineering and synthetic biology enable the production of these compounds. Several challenges remain including increasing carbon flux toward hydrocarbon fuel precursors in primary metabolism, increasing the low titers of hydrocarbons produced, and establishing robust host strains. Also, more fuel property testing of fungal-derived compounds individually or in fuel blendstocks is needed to determine the true potential of these compounds in liquid transportation fuels.