Insights into the evolution and drug susceptibility of Babesia duncani from the sequence of its mitochondrial and apicoplast genomes

Abstract

Babesia microti and Babesia duncani are the main causative agents of human babesiosis in the United States. While significant knowledge about B. microti has been gained over the past few years, nothing is known about B. duncani biology, pathogenesis, mode of transmission or sensitivity to currently recommended therapies. Studies in immunocompetent wild type mice and hamsters have shown that unlike B. microti, infection with B. duncani results in severe pathology and ultimately death. The parasite factors involved in B. duncani virulence remain unknown. Here we report the first known completed sequence and annotation of the apicoplast and mitochondrial genomes of B. duncani. We found that the apicoplast genome of this parasite consists of a 34 kb monocistronic circular molecule encoding functions that are important for apicoplast gene transcription as well as translation and maturation of the organelle's proteins. The mitochondrial genome of B. duncani consists of a 5.9 kb monocistronic linear molecule with two inverted repeats of 48 bp at both ends. Using the conserved cytochrome b (Cytb) and cytochrome c oxidase subunit I (coxI) proteins encoded by the mitochondrial genome, phylogenetic analysis revealed that B. duncani defines a new lineage among apicomplexan parasites distinct from B. microti, Babesia bovis, Theileria spp. and Plasmodium spp. Annotation of the apicoplast and mitochondrial genomes of B. duncani identified targets for development of effective therapies. Our studies set the stage for evaluation of the efficacy of these drugs alone or in combination against B. duncani in culture as well as in animal models.

Insights into the phylogenetic relationships and drug targets of Babesia isolates infective to small ruminants from the mitochondrial genomes

“…With the exception of B. conradae, piroplasm infective to the same host fell into one clade. These ndings are consistent with the phylogenetic position of B. gibsoni, B. duncani and B. orientalis based on the amino acid sequences of cox1 and cytb [26,27,30].…”

“…Studies of mitochondrial genomes could provide new insight into the biological features, genetic evolution and classi cation of the causative agents, as well as providing data for designing anti-Babesia compounds. To date, sequencing of the mitochondrial genomes has been performed for B. bigemina, Babesia bovis, B. caballi, B. canis, B. conradae, B. duncani, B. gibsoni, B. microti, B. orientalis, B. rodhaini, B. rossi, B. vogeli, Theileria equi and T. orientalis [26][27][28][29][30][31]. However, there are limited data on the mitochondrial genomes of ovine Babesia spp.…”

Insights into the phylogenetic relationships and drug targets of Babesia isolates infective to small ruminants from the mitochondrial genomes

“…However, one pair of TIRs was found in the mitochondrial genomes of other Babesia spp. and Theileria spp., ranging from 25 to 1563 bp in length [ 26 – 28 , 30 , 32 ]. These findings indicated that the number and size of TIRs are one of the main causes of different mitochondrial genome sizes.…”

Annotation and characterization of Babesia gibsoni apicoplast genome

“…Herein, we sequenced, assembled, annotated and characterized the apicoplast genome of B. gibsoni. The raw apicoplast genome sequence of B. gibsoni obtained from high throughput genome sequencing (data unpublished) was shown to have a circular form with a full length of 46 kb, which is bigger than that of any other reported Babesia apicoplast genome [22,23,[27][28][29]. To further verify the sequence, we adopted a primer-walking approach to test the B. gibsoni genomic DNA by designing a series of specific primers based on the amplicons covering the whole apicoplast genome (Additional file 1: Table S1, Additional file 2: Figure S1).…”