Coxiella endosymbionts of ticks
As in recent studies by Mwamuye et al. (2017) and Oundo et
al. (2020), we also obtained Coxiella endosymbiont sequences
from Rickettsia 16S rRNA primer amplicons. Previous studies have
shown that these endosymbionts, which are closely related to the
pathogen responsible for Q fever, C. burnetii, provide additional
essential nutrients and reproductive fitness to ticks. Their elimination
with antibiotic treatment was shown to negatively impact the fitness of
the lone star tick Amblyomma americanum (Zhong et al., 2007). The
phylogenetic co-divergence between the different tick species and their Coxiella endosymbionts shows the high specificity of these
endosymbionts to their tick hosts. Four phylogenetic clades (A-D) have
been described for tick-associated Coxiella endosymbionts. The
sequences of endosymbionts from this study fell into groups B and C.
Group B consists of Coxiella-endosymbionts of Amblyomma and Ornithodoros, while group C consists of rhipicephaline
endosymbionts (Duron et al., 2015). These endosymbionts are
non-pathogenic. However, it is important to note that there is evidence
that Coxiella burnetii evolved recently from a
maternally-inherited symbiont of ticks (Duron et al., 2015).