Comparative analysis of apicoplast genomes of Babesia infective to small ruminants in China

Xiaoxing Wang,Shuaiyang Zhao,Hong Yin,Jianlin Xu,Xin He,Junlong Liu,Zhi Li,Jianxun Luo,Jinming Wang,Guiquan Guan,Youquan Li,Aihong Liu

doi:10.1186/s13071-019-3581-x

Abstract

BackgroundBabesiosis is an economically important disease caused by tick-borne apicomplexan protists of the genus Babesia. Most apicomplexan parasites, including Babesia, have a plastid-derived organelle termed an apicoplast, which is involved in critical metabolic pathways such as fatty acid, iron-sulphur, haem and isoprenoid biosynthesis. Apicoplast genomic data can provide significant information for understanding and exploring the biological features, taxonomic and evolutionary relationships of apicomplexan parasites, and identify targets for anti-parasitic drugs. However, there are limited data on the apicoplast genomes of Babesia species infective to small ruminants.MethodsPCR primers were designed based on the previously reported apicoplast genome sequences of Babesia motasi Lintan and Babesia sp. Xinjiang using Illumina technology. The overlapped apicoplast genomic fragments of six ovine Babesia isolates were amplified and sequenced using the Sanger dideoxy chain-termination method. The full-length sequences of the apicoplast genomes were assembled and annotated using bioinformatics software. The gene contents and order of apicoplast genomes obtained in this study were defined and compared with those of other apicomplexan parasites. Phylogenetic trees were constructed on the concatenated amino acid sequences of 13 gene products using MEGA v.6.06.ResultsThe results showed that the six ovine Babesia apicoplast genomes consisted of circular DNA. The genome sizes were 29,916–30,846 bp with 78.7–81.0% A + T content, 29–31 open reading frames (ORF) and 23–24 transport RNAs. The ORFs encoded four DNA-directed RNA polymerase subunits (rpoB, rpoCl, rpoC2a and rpoC2b), 13 ribosomal proteins, one elongation factor TU (tufA), two ATP-dependent Clp proteases (ClpC) and 7–11 hypothetical proteins. Babesia sp. has three more genes than Babesia motasi (rpl5, rps8 and rpoB). Phylogenetic analysis showed that Babesia sp. is located in a separate clade. Babesia motasi Lintan/Tianzhu and B. motasi Ningxian/Hebei were divided into two subclades.ConclusionsTo our knowledge, this study is the first to elucidate the whole apicoplast genomic structural features of six Babesia isolates infective to small ruminants in China using Sanger sequencing. The data provide useful information confirming the taxonomic relationships of these parasites and identifying targets for anti-apicomplexan parasite drugs.

Highlights

Babesiosis is an economically important disease caused by tick-borne apicomplexan protists of the genus Babesia
Bioinformatics analysis indicated that the circular deoxyribonucleic acid (DNA) contained a small subunit and a large subunit ribosomal RNA (SSU and LSU), 23–24 transfer ribonucleic acids and five to six ribosomal protein large subunits, eight to nine ribosomal protein small subunits, four to five subunits of DNA-directed RNA polymerase, two ATP-dependent Clp proteases, one elongation factor TU, and seven to eleven hypothetical protein genes (Table 2)
The alignment of apicoplast genomes of ovine Babesia isolates indicated that the identities of Babesia sp. Xinjiang (BspXJ)/DH, B. motasi Lintan (BmLT)/TZ and B. motasi Ningxian (BmNX)/HB were 99.8, 99.9 and 99.9%, respectively

Summary

Introduction

Babesiosis is an economically important disease caused by tick-borne apicomplexan protists of the genus Babesia. Most apicomplexan parasites, including Babesia, have a plastid-derived organelle termed an apicoplast, which is involved in critical metabolic pathways such as fatty acid, iron-sulphur, haem and isoprenoid biosynthesis. Most apicomplexan protists cause important diseases of humans and other animals, including malaria (Plasmodium spp.), toxoplasmosis (Toxoplasma gondii), cryptosporidiosis (Cryptosporidium spp.), cyclosporiasis (Cyclospora cayetanensis), coccidiosis (Eimeria spp.), babesiosis (Babesia spp.), theileriosis (Theileria spp.) and neosporosis (Neospora caninum) [1]. These parasites, with the exception of Cryptosporidium spp. The apicoplast is involved in critical metabolic pathways such as fatty acid, iron-sulphur, haem and isoprenoid biosynthesis. The apicoplast and some of these metabolic pathways are vital for parasite survival, making the apicoplast an attractive target for anti-parasitic drugs

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Results

Discussion

Conclusion