Extensive diversity of Rickettsiales bacteria in two species of ticks from China and the evolution of the Rickettsiales

Abstract

BackgroundBacteria of the order Rickettsiales (Alphaproteobacteria) are obligate intracellular parasites that infect species from virtually every major eukaryotic lineage. Several rickettsial genera harbor species that are significant emerging and re-emerging pathogens of humans. As species of Rickettsiales are associated with an extremely diverse host range, a better understanding of the historical associations between these bacteria and their hosts will provide important information on their evolutionary trajectories and, particularly, their potential emergence as pathogens.ResultsNine species of Rickettsiales (two in the genus Rickettsia, three in the genus Anaplasma, and four in the genus Ehrlichia) were identified in two species of hard ticks (Dermacentor nuttalli and Hyalomma asiaticum) from two geographic regions in Xinjiang through genetic analyses of 16S rRNA, gltA, and groEL gene sequences. Notably, two lineages of Ehrlichia and one lineage of Anaplasma were distinct from any known Rickettsiales, suggesting the presence of potentially novel species in ticks in Xinjiang. Our phylogenetic analyses revealed some topological differences between the phylogenies of the bacteria and their vectors, which led us to marginally reject a model of exclusive bacteria-vector co-divergence.ConclusionsTicks are an important natural reservoir of many diverse species of Rickettsiales. In this work, we identified a single tick species that harbors multiple species of Rickettsiales, and uncovered extensive genetic diversity of these bacteria in two tick species from Xinjiang. Both bacteria-vector co-divergence and cross-species transmission appear to have played important roles in Rickettsiales evolution.

“Candidatus Finniella” (Rickettsiales, Alphaproteobacteria), Novel Endosymbionts of Viridiraptorid Amoeboflagellates (Cercozoa, Rhizaria)

“…Rickettsiales are obligate intracellular bacteria that colonize a broad range of eukaryotic hosts, including various arthropod and mammalian cells, leeches, nematodes, and cnidarians (9,65). Besides metazoan hosts, diverse protists harbor rickettsial endosymbionts as well (5,9,65). Previous analyses of molecular sequence data as well as our present results reveal that the rickettsial phylogeny is not congruent with the phylogeny of the host organisms, indicating a frequent lateral transfer of rickettsial endosymbionts between phylogenetically distant hosts (9,65).…”

“…Rickettsiales are obligate intracellular bacteria that colonize a broad range of eukaryotic hosts, including various arthropod and mammalian cells, leeches, nematodes, and cnidarians (9,65). Besides metazoan hosts, diverse protists harbor rickettsial endosymbionts as well (5,9,65).…”

“…Besides metazoan hosts, diverse protists harbor rickettsial endosymbionts as well (5,9,65). Previous analyses of molecular sequence data as well as our present results reveal that the rickettsial phylogeny is not congruent with the phylogeny of the host organisms, indicating a frequent lateral transfer of rickettsial endosymbionts between phylogenetically distant hosts (9,65). For pathogenic representatives such as Rickettsia, Anaplasma, and Ehrlichia, it is well established that these bacteria cycle between hosts on a regular basis (e.g., between an arthropod vector and a mammalian host), whereas most of the protist-colonizing Rickettsiales have been detected in single natural host species only.…”

“…Protists have even been suggested to serve as vectors and training grounds for pathogenic bacteria (6). They are frequently colonized by representatives of the eubacterial orders Chlamydiales (Chlamydiae), Legionellales (Gammaproteobacteria), and Rickettsiales (Alphaproteobacteria), whose members are linked to severe diseases in mammals, including humans (7)(8)(9).…”

The Bacteriome of Bat Flies (Nycteribiidae) from the Malagasy Region: a Community Shaped by Host Ecology, Bacterial Transmission Mode, and Host-Vector Specificity

“…The gltA locus of Rickettsia was amplified from Eucampsipoda madagascarensis and Penicillidia leptothrinax samples. Classification using BLASTx showed that the obtained gltA sequences showed little homology to known species of Rickettsia, with the strongest match showing 90% identity to gltA from Rickettsia raoultii, a bacterium identified in hard ticks from China (46). In addition, a 1,350-bp fragment of the 16S gene of Rickettsia was amplified from Eucampsipoda madagascarensis.…”