Abstract
Rickettsia are intracellular bacteria best known as the causative agents
of human and animal diseases. Although these medically important
Rickettsia are often transmitted via haematophagous arthropods, other
Rickettsia, such as those in the Torix group, appear to reside
exclusively in invertebrates and protists with no secondary vertebrate
host. Importantly, little is known about the diversity or host range of
Torix group Rickettsia. This study describes the serendipitous discovery
of Rickettsia amplicons in the Barcode of Life Data System (BOLD), a
sequence database specifically designed for the curation of mtDNA
barcodes. Out of 184,585 barcode sequences analysed, Rickettsia is
observed in approximately 0.41% of barcode submissions and is more
likely to be found than Wolbachia (0.17%). The Torix group of
Rickettsia are shown to account for 95% of all unintended
amplifications from the genus, with a multilocus analysis of these
strains revealing this symbiont commonly shifts between distantly
related host taxa. A further targeted PCR screen of 1,612 individuals
from 169 terrestrial and aquatic arthropod species identified mostly
Torix strains (14/16) and supports the “aquatic hotspot” hypothesis
for Torix infection. Furthermore, the analysis of Sequence Read Archive
(SRA) deposits indicates Torix infections represent a significant
proportion of all Rickettsia symbioses. This combination of methods
reveals a broad host diversity associated with Torix Rickettsia
including phloem-feeding bugs, parasitoid wasps, forest detritivores and
vectors of disease. The unknown host effects and transmission strategies
of these endosymbionts makes these newly discovered associations
important to inform future directions of investigation involving the
understudied Torix Rickettsia.