1. Department of Pediatrics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0760
2. Department of Chemical and Biomolecular Engineering, Metabolic Engineering and Systems Biology Laboratory, University of Delaware, 150 Academy Street, Newark, Delaware 19716
3. National Bioenergy Center, National Renewable Energy Laboratory, Golden, Colorado 80401
4. Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218