Mutualists and parasites: how to paint yourself into a (metabolic) corner

Eukaryotes have developed an elaborate series of interactions with bacteria that enter their bodies and/or cells. Genome evolution of symbiotic and pa rasitic bacteria multiplying inside eukaryotic cells results in both conver gent and divergent changes. The genome sequences of the symbiotic bacteria of aphids, Buchnera aphidicola, and the parasitic bacteria of body louse an d humans, Rickettsia prowazekii, provide insights into these processes. Con vergent genome characteristics include reduction in genome sizes and lowere d G+C content values. Divergent evolution was recorded for amino acid and c ell wall biosynthetic genes, The presence of pseudogenes in both genomes pr ovides examples of recent gene inactivation events and offers clues to the process of genome deterioration and host-cell adaptation. (C) 2001 Federati on of European Biochemical Societies. Published by Elsevier Science B,V, Al l rights reserved.