1 Microbes & Pathogen Biology, The Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, 19 Chlorine Gardens, Belfast BT9 5DL, UK. Electronic address: l.atkinson@qub.ac.uk.
2 Department of Microbiology, Immunology, and Molecular Genetics and Molecular Biology Institute, University of California, Los Angeles, 615 Charles E. Young Dr. S., Los Angeles, CA 90095, USA. Electronic address: ehallem@ucla.edu.