Date Published: April 5, 2012
Author(s): Natasha D Mallette, W Berk Knighton, Gary A Strobel, Ross P Carlson, Brent M Peyton.
Volatile hydrocarbon production by Ascocoryne sacroides was studied over its growth cycle. Gas-phase compounds were measured continuously with a proton transfer reaction-mass spectrometry (PTR-MS) and at distinct time points with gas chromatography-mass spectrometry (GC-MS) using head space solid phase microextraction (SPME). The PTR-MS ion signal permitted temporal resolution of the volatile production while the SPME results revealed distinct compound identities. The quantitative PTR-MS results showed the volatile production was dominated by ethanol and acetaldehyde, while the concentration of the remainder of volatiles consistently reached 2,000 ppbv. The measurement of alcohols from the fungal culture by the two techniques correlated well. Notable compounds of fuel interest included nonanal, 1-octen-3-ol, 1-butanol, 3-methyl- and benzaldehyde. Abiotic comparison of the two techniques demonstrated SPME fiber bias toward higher molecular weight compounds, making quantitative efforts with SPME impractical. Together, PTR-MS and SPME GC-MS were shown as valuable tools for characterizing volatile fuel compound production from microbiological sources.
Ascocoryne sarcoides is an endophytic fungus recently isolated from Northern Patagonia and has the potential to produce a petroleum-like fuel (Mycodiesel®) directly from a cellulose fermentation process [Strobel, Knighton, Kluck, Ren, Livinghouse, Griffin, Spakowicz and Sears 2008]. Fungi produce medium to long chain hydrocarbons, and the prevalence of these compounds is in the C19-C30 chain length [Ladygina, Dedyukhina and Vainshtein 2006]. In contrast, Ascocoryne sarcoides (NRRL 50072) has been reported to produce a series of straight chained and branched medium chain-length hydrocarbons of C5-C10 chain length, in the range of gasoline fuel, including heptane, 2-pentene, octane, 1-methyl-cyclohexene, 3,5-octadiene, and cyclodecene [Solomons and Fryhle 2002,Griffin, Spakowicz, Gianoulis and Strobel 2010]. This interesting metabolism requires further work to characterize growth patterns and develop the organism for potential biofuel applications.
Taken together, the results of the PTR-MS and SPME GC-MS techniques provide a more definitive description of the VOCs produced by A. sarcoides for product (e.g. biofuel) development. However, the challenges associated with the quantitative and qualitative analysis of complex VOC mixtures in an aqueous solution are non-trivial, and neither method had the ability to both identify and quantify the breadth of compound diversity synthesized by this complex fungal system.
GC-MS: Gas Chromatography – Mass Spectrometry; NIST: National Institute of Standards and Technology; PTR-MS: Proton Transfer Reaction – Mass Spectrometry; SPME: Solid Phase Microextraction; VOCs: Volatile Organic Compounds.
The authors declare that they have no competing interests.