Christopher Voigt at the University of California is genetically ‘hacking’ into the brewers yeast of ethanol fame to modify the yeast so its output isn’t ethanol but a methyl halide. The methyl halide switches over to a bio gasoline with a simple catalytic reaction. This is not a simple problem.

Voigt is targeting to use crop wastes, the leftovers from food production and grasses, which can be grown in areas not used for food production. Both materials are high in cellulose content and their use would avoid the food competition issue and offer more biomass to fuel production.

Voigt’s team was aware that some plants and microorganisms do make the desired methyl halides in small amounts using enzymes called methyl halide transferase enzymes. They also knew just a few were known – so the team set out to find more.

The effort involves scouring the DNA sequence databases for the genetic codes that provide for the proteins that make up the enzymes. That step started they asked a DNA synthesis firm to make up the 89 discovered matching genes. Those they spliced into the DNA of E. coli bacteria to learn which would produce the methyl halide most efficiently.

Voigt explained the work as, “We were essentially mining the sequence databases for function.”

The outstanding leader turned out to be one of the previously known methyl halide transferase genes, from Batis maritima, known as turtleweed or saltwort, a plant found in the salt marshes of the southeastern US and California. They then spliced the gene into yeast so to produce a strain able to make methyl halides in large amounts. Result – an alternative yeast for starch to fuel.

But, the team’s yeast is still not a cellulose digester even though they have a methyl halide producer. They are looking for an organism that digests cellulose into products the yeast can use for making the methyl halides.

That effort is underway across a very broad spectrum of research both in private companies and in universities. The known organisms are laboriously slow or must live at high temperatures or both.

What Voigt’s team has chosen is a bacterium called Actinotalea fermentans isolated in the 1980s from a landfill dump in France. It excretes acetate and if it is cultured alone, it soon poisons itself with this waste product. But yeast loves acetate as a food source.

With that the Voigt team seems to have the ideal microbial team, at lab scale. A. fermentans converts biomass cellulose into acetate, that is then made into methyl halides by the DNA hacked and engineered yeast. It’s a low-temperature, cheap process that produces the methyl halides that are readily catalytically convertible into biogasoline.

In a bold assertion as the team thinks their process will calculate such that it could produce gasoline more cheaply than from oil. They aren’t saying oil at what price, though. That assumes the system can be made to work at least as efficiently as yeast does in sugar to ethanol. The team is working on the efficiency, altering their yeast’s enzymes to tune its metabolism for higher productivity in the acetate to substrate for the methyl halide transferase to make the methyl halides.

Will this work, is it scaleable and other questions remain. It’s way to soon to tell now. Yet the background of the university, the Voigt Lab, and the previous work show that the microbiology field when seen in a ‘hacking’ mode for the redesign of the DNA has great potential across a wide range of science problems.

From a consumers point of view and as a practical matter for policy makers to commercial interests its best to get as many processes, approaches and concepts into development as possible. But a single process method from high cellulose biomass to biogasoline is quite an achievement for which Voigt and his team can be very proud.

A paper is up in the Journal of the American Chemical Society with the preliminary DOI of 10.1021.ja8094611u. It will be interesting to see of this process can scale up and what the economics turn out to be for commercial production.


7 Comments so far

  1. jp straley on April 24, 2009 8:08 AM

    AT large wastewater treatment plants, anaerobic reactors treat waste. They are best, of course, for carbohydrate waste.

    There are two suites of bacteria in these reactors, acetate producers and methanogens. The methanogens can only use little acids, up to three carbons.

    Presumeably, this system could be modified so that these reactors could produce the methyl halides in a scheme similar to that described in the article….then municipalities produce gasoline from wastewater!


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