Fatty acid esters are a potential bio-based alternative to petroleum-based diesel fuels. Microbial fermentation of fatty acids from simple sugars for biodiesel is an attractive production method because of the ease of genetic manipulation of many microbial hosts and the fast growth rates of certain microorganisms. However, drawbacks to current methods of microbial biofuel production exist, including the poor cold-flow properties of the fatty acid mixtures. Microbially-produced fatty acids consist of primarily straight-chain molecules which have high freezing points once esterified with short-chain alcohols. Increasing the percentage of unsaturated fatty acids can lower the freezing point but renders the fuel more reactive (susceptible to oxidation). On the other hand, incorporating branches into fatty acid chains can lower the overall freezing point while also increasing the fuel’s energy content. Some gram-positive bacteria, such as the Mycobacteria, naturally produce branched fatty acids, but their pathogenicity and the long length of their fatty acids (long fatty acids also freeze at high temperatures) render them non-ideal hosts for biofuels. Herein, we report the production of various branched fatty acids in Streptomyces, a genus of gram-positive Actinobacteria known for their production of diverse secondary metabolites. We chose Streptomyces as hosts for the production of biodiesel with lower freezing points because they naturally already produce iso- and anteiso-branched fatty acids, because of the recent development of a large suite of genetic tools for these organisms, and because they are non-pathogenic. We have engineered strains of Streptomyces sp. that produce fatty acids with mid-chain methyl branches and cyclopropyl groups by heterologously expressing methyltransferases from Mycobacteria and manipulating the host’s fatty acid metabolism. To the best of our knowledge, this is the first example of the use of Streptomyces as hosts for the heterologous production of fatty acids for biofuels.

Development of Streptomyces as heterologous hosts for the production of branched fatty acids for biofuels

253rd National Meeting (2017)

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