Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Effects of expressing the killer and antidote genes from the Bacillus subtilis spoIIS locus under the control of a xylose-inducible promoter. Xylose-containing filter squares were placed over Petri dishes plated with three different strains. The panels with dark backgrounds resulted from expression of both genes; the lawn of bacteria grew unaffected. The panels with isolated colonies growing around the filter resulted from expression of the killer gene alone; there was no bacterial growth except for spontaneous mutants. The panels showing a halo around the filter resulted from expression of the killer gene under xylose control and the antidote gene under its own promoter; next to the filter there is an excess of killer product, and the bacteria cannot grow. (See related article on page 3574.)