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.
Highlights
Human babesiosis is an emerging infectious disease caused by a select group of intraerythrocytic protozoan parasites defining a new clade in the Apicomplexan phylum distinct from those encompassing Plasmodium species, Theileria species or Babesia bovis [1]
Sequencing and assembly revealed that the apicoplast genome of B. microti is composed of a circular molecule of 28.7 kbp
The genome is 86% A+T rich and has a coding density of over 98%. It encodes SSU and LSU rRNAs, 18 ribosomal proteins, an EF-Tu elongation factor, three subunits of the RNA polymerase, 2 copies of the ClpC chaperone, 24 tRNAs and five hypothetical proteins ranging in size between 49 (Hyp-E) and 140 amino acids (Hyp-A) (Fig. 1)
Summary
Human babesiosis is an emerging infectious disease caused by a select group of intraerythrocytic protozoan parasites defining a new clade in the Apicomplexan phylum distinct from those encompassing Plasmodium species, Theileria species or Babesia bovis [1]. Human babesiosis is endemic in northeastern and northern midwestern United States but has been reported in Europe, Asia, Africa, Australia and South America [2,3]. Depending on their immune status and age, patients with human babesiosis can experience mild, moderate or severe illness with the latter possibly leading to multi-organ system failure and death. As a result babesiosis has been recognized as an emerging health threat [5], and since 2011 has been designated as a nationally notifiable disease by the Center for Disease Control [6]
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