Lateral Gene Transfer (LGT) between Archaea and Escherichia coli is a contributor to the emergence of novel infectious disease

Archeal-like genes acting as virulence genes are present in several pathogens and genomes contain a number of archaeal-like genes of unknown function. Archaea, by virtue of their very different evolutionary history and different environment, provide a pool of potential virulence genes to bacterial pathogens.We can test this hypothesis by 1)identifying genes likely to have been transferred (directly or indirectly) to E. coli O157:H7 from archaea; 2)investigating the distribution of similar genes in pathogens and non-pathogens and 3)performing rigorous phylogenetic analyses on putative transfers.Although this hypothesis focuses on archaea and E. coli, it will serve as a model having broad applicability to a number of pathogenic systems. Since no archaea are known vertebrate pathogens, archaeal-like transferred genes that are associated with virulence in bacteria represent a clear model for the emergence of virulence genes.The fact and process of lateral gene transfer (LGT) has been integral to the study of infectious disease since Griffith [1]. Most investigations have, however, centered on transfer of known virulence genes and genes involved in establishing infections (antibiotic resistance, toxins, capsule, etc.) between close relatives who are both pathogens. The explosion of gene sequence information and complete genomes in the last 5 years has reinforced and extended our view of virulence evolution. To quote a review [2]: "lateral transfers have effectively changed the ecological and pathogenic character of bacterial species." Analysis of gene sequence and complete genome information[3-11] have led to the realization that LGT is not a rare exception to classical Darwinian evolution, but may be the predominant mode of evolutionary change in prokaryotes[2,12-15].Given the common perception of archaea as extremophiles, one might expect the opportunity for transfer between archaeal organisms and bacterial pathogens to be a rare event. However, many archaea are presen