About the Authors
Howard Hughes Medical Institute and Division of Biology and Department of Applied Physics, California Institute of Technology, Pasadena, California, United States of America
Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America
The authors have declared that no competing interests exist.
The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: JHL MBE JD. Performed the experiments: JHL MEF. Analyzed the data: JHL MBE. Contributed reagents/materials/analysis tools: JHL MEF MBE. Wrote the paper: JHL MBE.