Abstract
The apicomplexan intraerythrocytic parasite Babesia microti is an emerging human pathogen and the primary cause of human babesiosis, a malaria-like illness endemic in the United States. The pathogen is transmitted to humans by the tick vector, Ixodes scapularis, and by transfusion of blood from asymptomatic B. microti-infected donors. Whereas the nuclear and mitochondrial genomes of this parasite have been sequenced, assembled and annotated, its apicoplast genome remained incomplete, mainly due to its low representation and high A+T content. Here we report the complete sequence and annotation of the apicoplast genome of the B. microti R1 isolate. The genome consists of a 28.7 kb circular molecule encoding primarily functions important for maintenance of the apicoplast DNA, transcription, translation and maturation of organellar proteins. Genome analysis and annotation revealed a unique gene structure and organization of the B. microti apicoplast genome and suggest that all metabolic and non-housekeeping functions in this organelle are nuclear-encoded. B. microti apicoplast functions are significantly different from those of the host, suggesting that they might be useful as targets for development of potent and safe therapies for the treatment of human babesiosis.