Digitally colorized scanning electron microscopic image depicting the amoeba Vermamoeba (Hartmannella) vermiformis (orange), as it entraps a Legionella pneumophila bacterium (green) with an extended pseudopod. After it is ingested, the Legionella pneumophila bacterium can survive as a symbiont within what then becomes its protozoan host. Under adverse environmental conditions, the amoeba is able to metamorphose into what is known as its cystic-stage, enabling it (and its symbiotic resident pathogen) to withstand such environmental stresses. Image by Barry S. Fields (Centers for Disease Control and Prevention, USA; Public Health Image Library, image ID #6640); image modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.