Supplementary Information Observing the Invisible through Imaging Mass Spectrometry, a Window into the Metabolic Exchange Capacity of Microbes David J. Gonzalez 9 *, Yuquan Xu 1 *, Yu-Liang Yang 1 *, Eduardo Esquenazi 1, 4 , Wei-Ting Liu 2 , Anna Edlund 4 , Tram Duong 1 , Liangcheng Du 3 , István Molnár 8 , William H. Gerwick 4 , Paul R. Jensen 4 , Michael Fischbach 5 , Chih-Chuang Liaw, Paul Straight 4 , Victor Nizet 1, 4,9 , Pieter C. Dorrestein 1, 2,4 1. Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego 2. Department of Chemistry and Biochemistry, University of California, San Diego 3. Department of Chemistry, University of Nebraska-Lincoln, Lincoln 4. Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego 5. Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco 6. Department of Biochemistry and Biophysics, Texas A&M University, College Station 7. Graduate Institute of Pharmaceutical Chemistry, College of Pharmacy, China Medical University, Taichung 404, Taiwan 8. Natural Products Center, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ 9. Department of Pediatrics, University of California, San Diego To whom correspondence should be directed: Prof. Pieter C. Dorrestein Skaggs School of Pharmacy and Pharmaceutical Sciences and Departments of Pharmacology, Chemistry and Biochemistry, Biomedical Science Building (BSB) Room 4090 9500 Gilman Drive, MC 0636 La Jolla, CA 92093-0636 Office: 858-534-6607 E-mail: pdorrest@ucsd.edu *D. J. Gonzalez, Y. Xu and Y-L. Yang contributed equally to this study.