MICROBIOLOGY. For the article “Self-generated diversity produces `insurance effects' in biofilm communities,” by Blaise R. Boles, Matthew Thoendel, and Pradeep K. Singh, which appeared in issue 47, November 23, 2004, of Proc. Natl. Acad. Sci. USA (101, 16630-16635; first published November 16, 2004; 10.1073/pnas.0407460101), the caption for the issue cover on page iii appeared incorrectly. The online version has been corrected. The corrected cover caption appears below.
Cover photograph: Bacterial colonies derived from a biofilm established from a pure culture of the opportunistic pathogen Pseudomonas aeruginosa. Biofilms are multicellular bacterial communities that cause many types of infection. After several days of biofilm growth, the resident bacteria undergo genetic diversification that strengthens the biofilm community. See the article by Boles et al. on pages 16630-16635. Photograph courtesy of T. O. Moninger, J. L. Kesselring, and P. K. Singh.