Whole-genome assembly of Babesia ovata and comparative genomics between closely related pathogens

Abstract

Background Babesia ovata, belonging to the phylum Apicomplexa, is an infectious parasite of bovids. It is not associated with the manifestation of severe symptoms, in contrast to other types of bovine babesiosis caused by B. bovis and B. bigemina; however, upon co-infection with Theileria orientalis, it occasionally induces exacerbated symptoms. Asymptomatic chronic infection in bovines is usually observed only for B. ovata. Comparative genomic analysis could potentially reveal factors involved in these distinguishing characteristics; however, the genomic and molecular basis of these phenotypes remains elusive, especially in B. ovata. From a technical perspective, the current development of a very long read sequencer, MinION, will facilitate the obtainment of highly integrated genome sequences. Therefore, we applied next-generation sequencing to acquire a high-quality genome of the parasite, which provides fundamental information for understanding apicomplexans.ResultsThe genome was assembled into 14,453,397 bp in size with 5031 protein-coding sequences (91 contigs and N50 = 2,090,503 bp). Gene family analysis revealed that ves1 alpha and beta, which belong to multigene families in B. bovis, were absent from B. ovata, the same as in B. bigemina. Instead, ves1a and ves1b, which were originally specified in B. bigemina, were present. The B. ovata and B. bigemina ves1a configure one cluster together even though they divided into two sub-clusters according to the spp. In contrast, the ves1b cluster was more dispersed and the overlap among B. ovata and B. bigemina was limited. The observed redundancy and rapid evolution in sequence might reflect the adaptive history of these parasites. Moreover, same candidate genes which potentially involved in the distinct phenotypes were specified by functional analysis. An anamorsin homolog is one of them. The human anamorsin is involved in hematopoiesis and the homolog was present in B. ovata but absent in B. bigemina which causes severe anemia.ConclusionsTaking these findings together, the differences demonstrated by comparative genomics potentially explain the evolutionary history of these parasites and the differences in their phenotypes. Besides, the draft genome provides fundamental information for further characterization and understanding of these parasites.Electronic supplementary materialThe online version of this article (10.1186/s12864-017-4230-4) contains supplementary material, which is available to authorized users.

Comparative analysis reveals conservation in genome organization among intestinal Cryptosporidium species and sequence divergence in potential secreted pathogenesis determinants among major human-infecting species

“…[26] or Babesia spp. [27]. Thus, compared with other apicomplexans, intestinal Cryptosporidium species have shown high genome conservation.…”

Novel Babesia bovis exported proteins that modify properties of infected red blood cells

“…SBP2 is also encoded by a multigene family, sbp2. Unlike ves1 and smorfs, which are unique to B. bovis, sbp2 are conserved across the genus Babesia [17][18][19]. SBP2 are localized to spherical bodies, organelles analogous to dense granules in other apicomplexan parasites, and are released into the RBC cytoplasm upon invasion [9].…”

Identification of proteins expressed by Babesia bigemina kinetes

“…While these three parasites species lacking a KSP gene undergo sexual reproduction in their arthropod vectors, none are transovarially transmitted. In contrast, the data suggest that all transovarially transmitted Babesia ( sensu stricto ) species, such as B. bovis , contain genes that are homologous to BbiKSP [7, 8, 13]. It is possible that BbiKSP encodes for a protein involved in parasite invasion into the ovaries and, thus, is required for transovarial transmission.…”