(328c) Using Synthetic Metagenomics to Discover Biocatalysts for Fuels Synthesis

The conversion of biomass to next generation fuels and chemicals will require the discovery and engineering of novel enzymes and metabolic pathways. We used a synthetic biology and metagenomics approach to discover enzymes that catalyze the formation of methyl halides, a reactive carbon building block that can be chemically converted to fuels and chemicals. A single methyl halide transferase (MHT) enzyme transfers the methyl group from the ubiquitous metabolite S-adenoyl methionine (SAM) to a halide ion.
Plants and microorganisms naturally produce methyl halides, but these organisms produce very low yields and are not amenable to industrial production. We used bioinformatics and chemical synthesis to identify and construct a library of 89 putative genes from sequence data in the NCBI database. The set was screened in Escherichia coli to identify the rates methyl halide production. We transferred the highest activity gene to yeast and re-engineered SAM pathway regulation to dramatically increase methyl halide productivity and conversion efficiency. Using a symbiotic co-culture of the engineered yeast and the cellulolytic bacterium Actinotalea fermentans, we are able to achieve methyl halide production from unprocessed switchgrass, corn stover, sugarcane bagasse, and poplar.
These results demonstrate the potential of producing methyl halides from non-food agricultural resources, and highlight strategies for discovering and optimizing novel routes for converting biomass to fuels and chemicals.