Virome Evolution (IMAGE) University of Pennsylvania School of Medicine Caption This is a phylogenetic tree of microphages detected in a PNAS study and other studies. The four microphage contigs with the highest substitution rates observed in the PNAS study are shown in large black lettering. The scale bar indicates the proportion of amino acid substitutions within the 919 amino acid major coat protein, which was aligned to make the tree. Credit Frederick Bushman, Ph.D., Perelman School of Medicine, University of Pennsylvania; <i>PNAS</i> Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.