| Summary: | <p>Abstract</p> <p>Background</p> <p>The <it>Rickettsia </it>genus includes 25 validated species, 17 of which are proven human pathogens. Among these, the pathogenicity varies greatly, from the highly virulent <it>R. prowazekii</it>, which causes epidemic typhus and kills its arthropod host, to the mild pathogen <it>R. africae</it>, the agent of African tick-bite fever, which does not affect the fitness of its tick vector.</p> <p>Results</p> <p>We evaluated the clonality of <it>R. africae </it>in 70 patients and 155 ticks, and determined its genome sequence, which comprises a circular chromosome of 1,278,540 bp including a <it>tra </it>operon and an unstable 12,377-bp plasmid. To study the genetic characteristics associated with virulence, we compared this species to <it>R. prowazekii</it>, <it>R. rickettsii </it>and <it>R. conorii</it>. <it>R. africae </it>and <it>R. prowazekii </it>have, respectively, the less and most decayed genomes. Eighteen genes are present only in <it>R. africae </it>including one with a putative protease domain upregulated at 37°C.</p> <p>Conclusion</p> <p>Based on these data, we speculate that a loss of regulatory genes causes an increase of virulence of rickettsial species in ticks and mammals. We also speculate that in <it>Rickettsia </it>species virulence is mostly associated with gene loss.</p> <p>The genome sequence was deposited in GenBank under accession number [GenBank: <ext-link ext-link-type="gen" ext-link-id="NZ_AAUY01000001">NZ_AAUY01000001</ext-link>].</p>
|
|---|
