1. Department
of Microbiology and Immunology, Harvard Medical School, Boston, Massachusetts 02115, United States
2. Department
of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States
3. Department
of Microbial Natural Products, Helmholtz-Institute for Pharmaceutical
Research Saarland (HIPS), Helmholtz Centre for Infection Research
(HZI), and Pharmaceutical Biotechnology, Saarland University, Campus E8.1, 66123 Saarbrücken, Germany