1. Department of Microbiology, University of Tennessee, Knoxville, TN 37996-0845, USA.
2. Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
3. Howard Hughes Medical Institute, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
4. Curriculum in Bioinformatics and Computational Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
5. Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
6. Joint Genome Institute, U.S. Department of Energy, Walnut Creek, CA, USA.
7. Carolina Center for Genome Sciences, University of North Carolina, Chapel Hill, NC 27599-3280, USA.