Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): A surface-rendered model of Prochlorococcus, an abundant marine cyanobacterium, which was visualized by cryo-electron tomography in a near-native state. Striking differences exist in the three-dimensional architecture of Prochlorococcus strains. MED4 (shown) belongs to a large clade comprised of recently differentiated lineages and has evolved a comparatively streamlined structure that includes an attenuated cell wall (blue) and less extensive intracytoplasmic membrane system (green) compared to the more deeply branched MIT9313 strain. A streamlined structure could be advantageous to microorganisms thriving in the low-nutrient conditions characteristic of large regions of the open oceans and thus have consequences for niche differentiation. (See related article on page 4485.)
[Table of Contents]