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International Collaboration Results in New, More Efficient Bioconversion Pathway

April 4, 2012

NREL, the Research Institute of Innovative Technology for the Earth (RITE), and Honda Research and Development (Honda R&D) have teamed together to uncover a novel pathway for the conversion of agricultural residues and other feedstocks to fuel ethanol. The research collaboration has developed and tested a new fermentation organism that efficiently processes both glucose and hemicellulose sugars.

A New Organism

The fermentation organism, Corynebacterium glutamicum, was developed by Dr. Hideaki Yukawa and his team at RITE, a renowned national research laboratory in Kyoto, Japan. Unlike common yeast or the NREL bacterial strain Zymomonas mobilis, this corynebacterium lives and grows in two distinct phases. In its aerobic growth phase, the strain grows rapidly in cell mass. When a high concentration of the organism is placed into an anaerobic (oxygen-deprived) setting, the organism population enters a resting state with very little growth. It, instead, serves as a type of biological catalyst, taking in sugars and producing ethanol. The RITE strain has been engineered to rapidly process not only glucose sugar, but also the major hemicellulose sugars — xylose and arabinose.

For the past five years, the strain's performance has been improved under a RITE/Honda joint research program. According to Honda, the ultimate goal of this research is to develop the process technology that will enable the production of low cost cellulosic ethanol. This will provide cost competitive liquid fuels for vehicles with much lower greenhouse gas emissions.

The Search for Inexpensive Sugars

In 2011, RITE and Honda R&D wanted an experienced research partner that could make inexpensive sugars, produced from lignocellulosic biomass, that were acceptable to the Japanese corynebacterium strain. RITE and Honda R&D approached NREL to enter into a research partnership. NREL provided standard, pretreated corn stover samples to RITE for testing. As a result of the initial samples, Honda funded NREL in November 2011 to prepare a wide range of pretreated corn stover lots, varying acid loadings (including no acid), pressure, and residence time in the pretreatment reactor. The varying pretreatment conditions meant there would be widely varying amounts of potential fermentation inhibitors (acetic acid, furfural, HMF, and others) in the different sample lots.

According to NREL's John Ashworth, fermentation trials conducted in Japan in January 2012, were both surprising and highly successful. After commercial enzymes were added to 12 NREL pretreated samples to produce simple sugars, the RITE strain was able to make use of all the major sugars and produce satisfactory ethanol yields in 20 - 40 hours. It did not appear to be significantly slowed by moderate or high levels of inhibitors, which might have occurred if it was growing rapidly or producing a great deal of cell mass.