Alkane Synthesis in the Genus Desulfovibrio

Abstract

Petroleum based transport fuels (PBTFs) are vital to both industrial and social prosperity. However, PTBFs are a finite resource and their combustion contributes significantly to greenhouse-gas emissions. Finding a sustainable, carbon neutral alterative to PBTFs is vital to sustain modern lifestyles and mitigate climate change. The only PBTF alternatives currently produced industrially are ethanol and fatty-acid methyl esters derived from food crops (first generation biofuels). First generation biofuels cannot be used directly in most current combustion engines and production methods threaten food sustainability. Advanced biofuels derived from synthetic biological pathways engineered into industrially tractable microorganisms would mitigate the constraints of first generation biofuels. The success of advanced biofuel research relies on identifying and characterising enzymes integral to microbial hydrocarbon production, which may be used to build optimal synthetic systems. The current study investigated alkane production in the genus Desulfovibrio with the aim of determining the alkane synthesis pathway and identifying critical enzymes. A screen of 21 Desulfovibrio strains, cultured in stable isotope labelled media, identified six alkane producing strains which synthesised mainly n-octadecane and n-eicosane. Due to the even chain length alkanes produced, a reductive pathway with full carbon conservation was hypothesised. Identification of alkanes in the cell lysate of several Desulfovibrio strains allowed proteins associated with alkanes to be narrowed down by fractionating cell lysate, followed by GC/MSD and protein analysis of each fraction. 2D-DIGE was employed to separate individual proteins and allow the protein profile of alkane containing cell lysate fractions to be compared to non-alkane containing fractions. In this way several hypothetical proteins that may be involved in Desulfovibrio alkane synthesis were identified.