Optimization of feedstock to fuel conversion in next-generation biofuels
Efficient and economical conversion of cellulose and starch in biomass into fermentable sugars poses as a major challenge to realizing the next generation of biofuels. Current requirement of exogenously added enzymes adds substantially to the cost of biofuel production from most plant biomass. Strategies aiming to overcome this important limitation include improvements in the manufacturing efficiency for recombinant proteins and the use of "energy plants" that have altered chemical properties such as decreased lignin.
In the Lam lab, a genetic engineering approach is taken to create "Smart Plants" that will produce the necessary enzymes needed for the efficient conversion of their own starch and cellulose into fermentable sugars. The current strategy is to optimize transgenic expression of key enzymes for cellulose breakdown such as fungal xylanase, laccase and lignin peroxidase through subcellular targeting. Both nuclear and plastid engineering approaches, together with protein design for desired enzyme characteristics, will be deployed to achieve high levels of protein expression with minimal physiological effects on the transformed plants. In addition to engineering target feedstocks such as sugarcane and cassava, a "Mix-Stock" approach has also been proposed as a more flexible deployment strategy (Lam et al., 2009 and Xin et al., 2009). In this scenario, easy-to-transform plant species such as tobacco will be used as the "enzyme stock plant" to provide the high level of enzymes needed for biomass breakdown and conversion. This approach is also being tested in the Lam Lab using the starch to sugar conversion enzymes as test cases.
The Rutgers Duckweed Stock Cooperative
Duckweeds are small aquatic plants found worldwide in lakes and waterways. They thrive on high levels of nitrogen and phosphates and can proliferate on municipal and agricultural run-offs. As such, they have been used for environmental monitoring by the EPA as well as commercially for low-cost remediation of water quality worldwide, especially in developing countries. Due to their small stature that requires minimal vascular architecture, duckweeds have soft tissue with little lignin. Coupled with their high rates of biomass increase (up to twice that of crop plants) and distinct habitats that minimize competition with food crops, these properties make duckweeds an attractive source of biomass to consider for biofuel production.
Rutgers researchers are actively investigating duckweeds as an integrated solution for global environment and energy demands. Two major efforts are currently underway at Rutgers: In the first, the genome of Greater Duckweed (Spirodela polyrhiza), with a genome size of ~150 Mb, is currently being sequenced with an international effort led by the Waksman Institute of Microbiology and with support through the Department of Energy's JGI (Joint Genome Initiative). More recently, a Rutgers Duckweed Cooperative with over 530 strains collected worldwide has been established at the Biotechnology Center for Agriculture and the Environment. Under its first Director Eric Lam, this Duckweed Cooperative will seek to promote and develop duckweed as a model aquatic plant for environmental remediation and biomass production. In addition to providing a centralized resource for the growing Duckweed community by maintaining and distributing various strains, the Cooperative will begin efforts to tap into the large genetic diversity that is likely represented in this collection. This will include systematic comparison of the duckweed strains for their metabolite content and growth characteristics under a variety of environmental conditions. A website for this community resource will be forthcoming to facilitate access to the resources and information that are being generated by duckweed researchers within and outside of Rutgers.