The funding announcement provides an overview of the problem:

A process based on the fermentation of pentose sugars (in the hydrolyzate) combined with the fermentation of glucose (derived from the saccharification of cellulose) is referred to as simultaneous saccharification and co-fermentation (SSCF). Currently both of these approaches face one or both of the following challenges.

First, both the saccharification and fermentation steps are hindered by toxins and inhibitors present in the hydrolyzate. Second, the fermentation of almost all the available six-carbon (C6) and five-carbon (C5) sugars to ethanol is vital to the overall economics of these processes. Currently, the cost effective conversion of all sugars by a fermentative organism to ethanol is not available.

Clearly organisms exist that can ferment the various sugars derived from lignocellulosic hydrolysis. However, the ability of the organisms to ferment hexose and pentose sugars equally well either simultaneously or sequentially has not been optimized. Often the conversion rates are low for C5 sugars and the costs for running two separate fermentation processes (one for C6 sugars and one for C5 sugars) are too high.

There are several novel approaches being examined by the biotechnology community to address these barriers in the cost-effective conversion of lignocellulosic sugars to ethanol and bioproducts. One key to the success of these approaches is the development of a fermentative organism that meets certain performance criteria. Base strains that could be adapted for specific process schemes are needed on a widely available basis. Such strains need to be able to convert a wide range of sugars at rates, yields and titers commensurate with production strain requirements and tolerate the potentially inhibitory environment of pretreated lignocellulosic biomass.

DOE has identified the following critical parameters necessary for the development of a cost-competitive process:

1. High yield or, equivalently, full sugar utilization with minimal byproduct formation;
2. High final ethanol titer;
3. High overall volumetric productivity;
4. Tolerance to inhibitors present in hydrolyzates; and
5. Affordable microbial systems

Therefore, for the successful deployment of commercial biomass-to-ethanol biorefineries, fermentation organisms must be improved so that they function in an inhibitory environment with high concentrations of sugars and other compounds including ethanol, at reasonable cost.

Because the goal is to build a high-volume cellulosic ethanol industry (60 billion gallon demand projected in 2030), applicants must identify the target “high-impact” feedstock: one that is sustainable at quantities exceeding 100 million tons per year.

Although fermentation is only one of several integral steps in converting lignocellulosic biomass to ethanol, the DOE funding will not pay with these project funds for process improvements in any area other than the improvement of the fermentative organism. Applicants may use their own funds outside of cost share for improvements in the other process steps. Funds are prohibited for organism discovery, or basic research leading to organism development.

Participating companies must be willing and able to commercialize the organisms they develop and must have a sound business strategy to license and market the organisms. DOE expects an additional $10 million in fiscal years 2008 and 2009 for this initiative, subject to congressional appropriations.

Resources:

• Development of Robust, Highly Efficient Fermentative Organisms for the Conversion of Lignocellulosic Biomass to Ethanol