Living Microbial Fossils


Genome sequencing of bacteria that have been living in unicellular organisms since primeval times revealed novel insights into the evolution of major bacterial pathogens of humans.
The first complete genome sequence of a bacterium that lives as a symbiont inside amoebae was recently determined by researchers at the Technische Universität München (Germany) and the University of Vienna (Austria).
The investigated bacteria have only recently been discovered and represent the closest living relatives of chlamydiae, according to Michael Wagner and Matthias Horn, lead authors of the study. Chlamydiae are among the most successful bacterial pathogens of humans and cause more than 60 million infections per year.
Deciphering the genetic material of the chlamydia-related symbiont allowed reconstruction of the biology and genetic make-up of the last common ancestor of the symbiont and pathogenic chlamydiae, which had lived in the Precambrian some 700 million years ago. The chlamydial ancestor was already dependent on an animal or plant host cell, presumably an ancient primitive unicellular organism. Long before the first vertebrates roamed the earth, primeval chlamydiae were colonising protozoa and exploiting them as host cells. Today these same strategies of host colonization enable modern chlamydiae and other bacterial pathogens to infect animals and humans. Protozoa (such as amoeba) should thus not be considered merely as predators feeding on bacteria, but also as key players in the evolution of important contemporary pathogens.
The research will be published on 08. April 2004 in Sciencexpress ( and shortly thereafter in the printed version of the journal Science Magazine (Science 304, 728-730).