UCSF engineers microbes to produce methyl halides

By Susanne Retka Schill
Researchers at the University of California, San Francisco, have published a paper on their work with a bacteria and a yeast that have the potential to become a truly feedstock flexible process producing an intermediate chemical new to the biomass industry. Christopher Voigt, an associate professor in pharmaceutical chemistry at UCSF, was the principle investigator for the paper, "Synthesis of Methyl Halides from Biomass Using Engineered Microbes," published online April 20 by the Journal of the American Chemical Society. http://pubs.acs.org/doi/abs/10.1021/ja809461u

"When we set up the project we were looking at introducing flexibility into biorefining," Voigt said. "In corn-to-ethanol, corn is the only feedstock and ethanol the only product." In the UCSF process, the engineered bacteria/yeast duo have successfully converted sugarcane bagasse, corn stover, switchgrass and poplar into methyl halide. While methyl halides are produced in nature at usually low volumes, it is a chemical familiar to the petrochemical industry that can be used in solvents, propellants and soil fumigants. Methyl halides can be manufactured into gasoline, olefins, aromatics, alcohols, ethers and other chemicals using zeolite catalysts common in the petroleum industry. The technology has been around since the 1970s and most often studied as a process for converting natural gas to gasoline, Voigt said, although it has not been tested at large scales.

The paper outlines the UCSF research using synthetic metagenomics to identify and select enzymes that were then genetically engineered into brewer's yeast to produce methyl halides instead of alcohol. The researchers grew their engineered yeast with a cellulose-eating bacteria originally isolated in the early 1980s from a French landfill. The bacteria was briefly considered for the cellulose-to-ethanol process but discarded when ethanol yields were relatively low and the dominant product, acetate, not as useful. In the UCSF process, the yeast consumes the bacteria's products in a symbiotic relationship providing a novel conversion of biomass to the intermediate chemical.

Several aspects of the process promise an energy efficient conversion process: the biomass is simply chopped finely and not chemically pre-processed; the microbes grow nicely at 30 degrees Celsius (86 degrees Fahrenheit); and, the methyl halides come off as a gas. The research team is now working on improving yields and rates. "Right now the process is 40-fold slower than the sugar to ethanol process," Voigt said. Work will also need to be done on the scalability of the fermentation and chemical catalysis of the methyl halide. The researchers have formed Biomex Inc. to help with the commercialization as their work proceeds, although the corporation is unfunded at this time.