Cellulose to Sugars Using Engineered Stealth Enzymes

GCC
A new enzyme engineering technology promises to provide abundant, cheap sugars in temperate climates, for conversion to fuels, chemicals, plastics, and feeds. Agrivida Inc. and Syngenta Ventures are collaborating on a plant cell wall engineering technology which promises to provide abundant sugars from biomass. The engineered biomass will come from altered maize, sorghum, miscanthus, switchgrass, and other forms of grass. The enzymes which will hydrolyse cellulose to sugars, will be built into the plants themselves, and only activated under specific, carefully controlled conditions.

In July, Agrivida announced breakthroughs in its development of sugar production from enzyme-expressing crops at the annual BIO industry conference, which followed recent awards from the US Department of Agriculture (USDA) (earlier post) and Advanced Research Projects Agency–Energy (ARPA–E) (earlier post) to further develop its proprietary technology platforms in sorghum and switchgrass.

The results reported at the BIO meeting showed increased cell wall degradation by up to 100% compared to non-engineered plants, while significantly decreasing enzyme loadings, following a mild pretreatment and heat activation. The study presented at the meeting determined that embedding Agrivida’s engineered enzymes in the cell walls of the crops was an effective strategy for improving the biofuels processing characteristics of the plants and dramatically decreasing external enzyme loadings, while still protecting the plants’ development and growth the scientists said. The study compared the appearance, processing characteristics, and other parameters of the intein-modified plants with non-engineered, native plants.

Agrivida transgenic corn stover was demonstrated in this study to have a conversion of more than 60 percent of cellulose to glucose, compared to approximately 30 percent seen with the control plants. Further, the enzyme loadings used with Agrivida’s engineered plants can be reduced well over 50 percent and still provide improved performance relative to the full enzyme loadings on non-engineered plants, thereby significantly lowering external enzyme requirements. Our new data provide additional proof that Agrivida transgenic crops can facilitate cellulose degradation in a way that greatly reduces the need for hydrolytic enzymes and expensive pretreatment processes. This capability suggests that cellulosic ethanol production can be greatly expanded at lower costs and with fewer emissions, chemicals, and other downstream requirements.

—Michael Raab, Ph.D., President of Agrivida

The ability to reduce external enzyme requirements is a critical development that should help enable the growth of the cellulosic biofuels industry, Raab says. In the absence of such technology, the external enzyme production capacity build-out required to meet the US Renewable Fuels Standard would exceed a cost of $5 billion. Agrivida’s plant traits aim to eliminate those enzyme production costs for producers.

In earlier studies, Agrivida had reported that embedding CWD enzymes in plant material during the growth phase enables more efficient processing of biomass by initiating hydrolysis of plant polysaccharides from within the plant. _GCC

The requirement to add costly exogenous enzymes to cellulosic biomass, for conversion to sugars) has driven the cost of cellulosic biofuels out of the realm of profitability for years. Some companies are developing microbes capable of converting cellulose to sugars, others are developing better enzymes or solid-state forms of enzymatic conversion which helps extend the economic life of the enzymes.

The Agrivida approach requires significant genetic modification of the plants themselves, which is apt to run into faux environmental opposition along the way. Still, the economic benefits of being able to grow high yield grass crops in temperate climates -- and being able to achieve a yield of sugar comparable to the finicky water-hog sugar cane -- are significant and motivating goals.