Cover photograph:Transmission electron micrographs of nonmucoid (PAO1) and mucoid (mucA22) strains of Pseudomonas aeruginosa. (Assistance with processing images provided by Judy Whittimore, East Tennessee State University, Johnson City, TN.) (See related article in September 2017, vol. 199, no. 18, e00048–17.) (Copyright © 2017 American Society for Microbiology. All Rights Reserved.)