Novel Chlamydiales genotypes identified in ticks from Australian wildlife

Abstract

BackgroundMembers of the order Chlamydiales are known for their potential as human and veterinary bacterial pathogens. Despite this recognition, epidemiological factors such as routes of transmission are yet to be fully defined. Ticks are well known vectors for many other infections with several reports recently describing the presence of bacteria in the order Chlamydiales in these arthropods. Australian wildlife are hosts to an extensive range of tick species. Evidence is also growing that the marsupial hosts these ticks parasitise can also be infected by a number of bacteria in the order Chlamydiales, with at least one species, Chlamydia pecorum, posing a significant conservation threat. In the current study, we investigated the presence and identity of Chlamydiales in 438 ixodid ticks parasitizing wildlife in Australia by screening with a pan-Chlamydiales specific targeting the 16S rRNA gene.ResultsPan-Chlamydiales specific PCR assays confirmed the common presence of Chlamydiales in Australian ticks parasitising a range of native wildlife. Interestingly, we did not detect any Chlamydiaceae, including C. pecorum, the ubiquitous pathogen of the koala. Instead, the Chlamydiales diversity that could be resolved indicated that Australian ticks carry at least six novel Chlamydiales genotypes. Phylogenetic analysis of the 16S rRNA sequences (663 bp) of these novel Chlamydiales suggests that three of these genotypes are associated with the Simkaniaceae and putatively belong to three distinct novel strains of Fritschea spp. and three genotypes are related to the “Ca. Rhabdochlamydiaceae” and putatively belong to a novel genus, Rhabdochlamydia species and strain, respectively.ConclusionsSequence results suggest Australian wildlife ticks harbour a range of unique Chlamydiales bacteria that belong to families previously identified in a range of arthropod species. The results of this work also suggest that it is unlikely that arthropods act as vectors of pathogenic members of the family Chlamydiaceae, including C. pecorum, in Australian wildlife. The biology of novel Chlamydiales identified in arthropods remain unknown. The pathogenic role of the novel Chlamydiales identified in this study and the role that ticks may play in their transmission needs to be explored further.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-1994-y) contains supplementary material, which is available to authorized users.

Molecular evidence of Chlamydia pecorum and arthropod-associated Chlamydiae in an expanded range of marsupials

“…In the current study, a pan- Chlamydiales order specific 16S rRNA gene PCR screening strategy provided molecular evidence that a range of other Australian marsupials also carry C. pecorum . A distinct range of novel bacteria from the order Chlamydiales were also found, some of which have been previously reported in ticks 18 , 19 , including those found parasitising Australian marsupials 13 .…”

“…“Uncultured Chlamydiales ” were previously described as the most abundant taxa in non-koala marsupials, even in smaller screens 10 , 11 , with the impact of these infections on animal health still unknown. Compared to the previous studies, the majority of the novel CRBs identified from marsupials in this study, however, are thought to primarily be limited to infections of arthropods 13 , 18 , 23 , 24 . Indeed, the predominant CRB sequence detected was a partial Ca .…”

“…Rhabdochlamydia porcellionis genotype 1) detected in this study was 100% identical to a recently described novel Ca . Rhabdochlamydia porcellionis genotype (KX774317) detected in marsupial-feeding tick species removed from koalas 13 . This genotype is previously described as having 98% BLAST similarity to Ca .…”

“…1 , Table 2 ) as well as previously described novel Ca . Rhabdochlamydia genotypes identified in ticks 13 .

Figure 4 Phylogenetic relationships of Ca .

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“…It is possible that C. pecorum is a naturally occurring organism within Australia’s marsupial species and the importation of livestock has selectively exacerbated its impact on koala populations 1 . More recently, preliminary investigations of tick species feeding on koalas and other Australian marsupials highlighted a diversity of novel CRBs, raising questions over the presence and impact of these novel bacteria on the marsupial host parasitised as well 13 .…”