Methyl Halides Made From Raw Biomass

With an eye toward producing commodity chemicals from nonfood biomass rather than petroleum, Christopher A. Voigt and coworkers of the University of California, San Francisco, have engineered baker's yeast to synthesize methyl halides (J. Am. Chem. Soc. 2009, 131, 6508). Plants and microorganisms naturally use methyl halide transferase (MHT) to pluck the methyl group from S-adenosyl methionine and combine it with a halide ion to make small amounts of methyl halides for various purposes. To beef up such production of methyl halides, which are used commercially as agricultural fumigants and in industrial chemical and fuel production, Voigt's group searched an NIH genetic sequence database and used automated chemical DNA synthesis to identify and make 89 MHT genes from plants, fungi, bacteria, and unidentified organisms. They screened the genes and incorporated those with the highest MHT activity into Saccharomyces cerevisiae. The engineered yeast produces a mix of methyl halides from sugars and sodium halide salts. By coculturing the yeast with the cellulose-degrading bacterium Actinotalea fermentans, which makes acetate and ethanol for the yeast to consume, the researchers produced methyl halides directly from unprocessed switchgrass, corn stover, and other plant material.