Cover photograph: (Top) Salt crystals harboring the halophilic archaeon Haloferax volcanii. The pink color results from production of the bacterioruberin pigment in H. volcanii. Clear crystals contain an H. volcanii mutant that lacks bacterioruberin. (Bottom) H. volcanii colonies with mutations that affect pigment production. Opsins in halophilic archaea may inhibit bacterioruberin synthesis to promote synthesis of the opsin cofactor retinal. (Photo courtesy of Serena M. Graham, Colby College.) (See related article in November 2017, vol. 199, no. 21, e00303–17.) (Copyright © 2017 American Society for Microbiology. All Rights Reserved.)