8-43: Fungal Processes for Direct Bioconversion of Cellulose to Hydrocarbons

Beyond characterization of cellulolytic fungal enzymes, very little research has examined the potential role of fungi in renewable fuel production. Ascocoryne sarcoides (NRRL 50072) is an endophytic fungus that can utilize cellulose as its sole carbon source. This fungus excretes "myco-diesel", a mixture of straight and branched chain hydrocarbons of C₅-C₁₀ chain length, in the range of gasoline and aviation fuel, including heptane, 2-pentene, octane, 1-methyl-cyclohexene, 3,5-octadiene, and cyclodecene (Griffin et al. 2010). Experimental results from shake flask and 5 liter reactor runs have verified hydrocarbon compound production under a wide array of growth conditions. Biomass yields in liquid culture have improved from 0.05 g/L to 4.8 g/L through medium improvements. The pH tolerance of A. sarcoides is in the acidic range, and optimal temperature is between 16-23^oC. Volatiles are released by the fungus throughout its growth cycle and have reached 2 ppm using glucose as a substrate (Mallette et al. 2012). Growth on cellulose produced a higher number of fuel-related hydrocarbons including alkanes and aromatics than growth on glucose. Future research will focus on combining knowledge of genetics with metabolic modeling to develop a deeper understanding of how A. sarcoides and other fungi are able to produce these fuel compounds from cellulosic substrates.