Have archaeal genes contributed to bacterial virulence?
Uri Gophna, Robert L. Charlebois and W. Ford Doolittle
Trends in Microbiology 2004, 12:213-219
Although archaea have not been described as pathogens, it
has recently been suggested that genes transferred from
archaea might specifically contribute to bacterial
virulence. Here, we survey 73 genomes of bacterial pathogens
for the presence of genes originating from archaea. We
describe 43 cases in which acquisition of archaeal genes by
bacterial pathogens can be demonstrated. Although no bona
fide virulence factors are among these acquired genes,
several of them probably affect pathogen-host interactions.
Archaea are as diverse as bacteria and as widely distributed
around the world. It is therefore mysterious that there are
no diseases of archaeal origin. Eckburg and colleagues [1]
have recently reasoned that such disorders might have been
systematically overlooked, whereas Faguy [2] has suggested a
different context in which archaea could be relevant to
disease: as donors through lateral gene transfer (LGT) of
virulence-promoting genes to pathogenic bacteria. When the
genome of Escherichia coli O157:H7 was compared with that of
K12, half a dozen O157:H7-specific genes could be recognized
as having been derived from archaea [2]. In one case, an
indirect argument for a role in infectivity or virulence
could be made. Faguy argued on a more general basis that,
for truly novel innovations in pathogenesis, bacteria might
have often dipped into the archaeal gene pool. The idea has
an unconventional appeal and would support claims for the
medical relevance in studying archaea. There are
nevertheless two reasons to be skeptical of such a notion.
First, the divergence between bacteria and archaea is
believed to be ancient and reflected in significant
structural and biochemical differences between them,
differences that should make successful LGT difficult. In
particular, archaeal proteins involved in transcription and
the DNA signals they recognize resemble their eukaryotic
homologs much more than their bacterial counterparts (for
reviews see Refs [3,4] ). Nevertheless, recent sequencing of
archaeal and bacterial genomes has shown that inter-domain
transfer is not uncommon [5,6] and in some extreme cases
even rampant. Consequently, a large fraction of Thermotoga
maritima genes appears to have archaeal origins [7,8] , and
the archaeon Methanosarcina mazei bears a multitude of bacterial-
derived genes, comprising up to a third of its genome [9].
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Comment: These findings might point to the evolutionary
order of single celled animals.
Posted by Robert Karl Stonjek.