The bacterial biome of ticks and their wildlife hosts at the urban–wildland interface
Authors: Egan Siobhon L. , Taylor Casey L. , Banks Peter B. , Northover Amy S. , Ahlstrom Liisa A. , Ryan Una M. , Irwin Peter J. , Oskam Charlotte L. 
Published: December 2021

Advances in sequencing technologies have revealed the complex and diverse microbial communities present in ticks (Ixodida). As obligate blood-feeding arthropods, ticks are responsible for a number of infectious diseases that can affect humans, livestock, domestic animals and wildlife. While cases of human tick-borne diseases continue to increase in the northern hemisphere, there has been relatively little recognition of zoonotic tick-borne pathogens in Australia. Over the past 5 years, studies using high-throughput sequencing technologies have shown that Australian ticks harbour unique and diverse bacterial communities. In the present study, free-ranging wildlife (n=203), representing ten mammal species, were sampled from urban and peri-urban areas in New South Wales (NSW), Queensland (QLD) and Western Australia (WA). Bacterial metabarcoding targeting the 16S rRNA locus was used to characterize the microbiomes of three sample types collected from wildlife: blood, ticks and tissue samples. Further sequence information was obtained for selected taxa of interest. Six tick species were identified from wildlife: Amblyomma triguttatum, Ixodes antechini, Ixodes australiensis, Ixodes holocyclus, Ixodes tasmani and Ixodes trichosuri. Bacterial 16S rRNA metabarcoding was performed on 536 samples and 65 controls, generating over 100 million sequences. Alpha diversity was significantly different between the three sample types, with tissue samples displaying the highest alpha diversity (P<0.001).

Proteobacteria

was the most abundant taxon identified across all sample types (37.3 %). Beta diversity analysis and ordination revealed little overlap between the three sample types (P<0.001). Taxa of interest included

Anaplasmataceae

,

Bartonella

,

Borrelia

,

Coxiellaceae

,

Francisella

,

Midichloria

,

Mycoplasma

and

Rickettsia

.

Anaplasmataceae

bacteria were detected in 17.7% (95/536) of samples and included

Anaplasma

,

Ehrlichia

and

Neoehrlichia

species. In samples from NSW, ‘Ca. Neoehrlichia australis’, ‘Ca. Neoehrlichia arcana’,

Neoehrlichia

sp. and

Ehrlichia

sp. were identified. A putative novel

Ehrlichia

sp. was identified from WA and

Anaplasma platys

was identified from QLD. Nine rodent tissue samples were positive for a novel

Borrelia

sp. that formed a phylogenetically distinct clade separate from the Lyme

Borrelia

and relapsing fever groups. This novel clade included recently identified rodent-associated

Borrelia

genotypes, which were described from Spain and North America.

Bartonella

was identified in 12.9% (69/536) of samples. Over half of these positive samples were obtained from black rats (Rattus rattus), and the dominant bacterial species identified were

Bartonella coopersplainsensis

and

Bartonella queenslandensis

. The results from the present study show the value of using unbiased high-throughput sequencing applied to samples collected from wildlife. In addition to understanding the sylvatic cycle of known vector-associated pathogens, surveillance work is important to ensure preparedness for potential zoonotic spillover events.