1. Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA 94305, USA.
2. Howard Hughes Medical Institute (HHMI), Stanford University, 371 Serra Mall, Stanford, CA 94305, USA.
3. Department of Global Ecology, Carnegie Institution for Science, 260 Panama Street, Stanford, CA 94305, USA.
4. U.S. Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA.