Cover photograph (Copyright © 2008, American Society for Microbiology. All Rights Reserved.): Symbiont discrimination in a nematode intestine. Shown is the insect-parasitic nematode Heteorhabditis bacteriophora containing transient Escherichia coli cells (green) and a biofilm of symbiotic Photorhabdus temperata cells (red). Only cells that form a biofilm on the posterior intestine persist to later invade the rectal gland cells before being released to nematode offspring developing inside the maternal body cavity. (See related article on page 2275.)See erratum