About the Authors
Department of Microbiology, Institute for Genomic Biology, University of Illinois, Urbana, Illinois, United States of America
Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: JE SB. Performed the experiments: VG HP SK RB. Analyzed the data: VG HP SK SB. Contributed reagents/materials/analysis tools: VG. Wrote the paper: JE SB.