title: Low level of sequence diversity at merozoite surface protein-1 locus of Plasmodium ovale curtisi and P. ovale wallikeri from Thai isolates.
abstract: BACKGROUND
  The merozoite surface protein-1 (MSP-1) is a candidate target for the development of blood stage vaccines against malaria. Polymorphism in MSP-1 can be useful as a genetic marker for strain differentiation in malarial parasites. Although sequence diversity in the MSP-1 locus has been extensively analyzed in field isolates of Plasmodium falciparum and P. vivax, the extent of variation in its homologues in P. ovale curtisi and P. ovale wallikeri, remains unknown.
  
  
  RESULTS
  Analysis of the mitochondrial cytochrome b sequences of 10 P. ovale isolates from symptomatic malaria patients from diverse endemic areas of Thailand revealed co-existence of P. ovale curtisi (n = 5) and P. ovale wallikeri (n = 5). Direct sequencing of the PCR-amplified products encompassing the entire coding region of MSP-1 of P. ovale curtisi (PocMSP-1) and P. ovale wallikeri (PowMSP-1) has identified 3 imperfect repeated segments in the former and one in the latter. Most amino acid differences between these proteins were located in the interspecies variable domains of malarial MSP-1. Synonymous nucleotide diversity (πS) exceeded nonsynonymous nucleotide diversity (πN) for both PocMSP-1 and PowMSP-1, albeit at a non-significant level. However, when MSP-1 of both these species was considered together, πS was significantly greater than πN (p<0.0001), suggesting that purifying selection has shaped diversity at this locus prior to speciation. Phylogenetic analysis based on conserved domains has placed PocMSP-1 and PowMSP-1 in a distinct bifurcating branch that probably diverged from each other around 4.5 million years ago.
  
  
  CONCLUSIONS
  The MSP-1 sequences support that P. ovale curtisi and P. ovale wallikeri are distinct species. Both species are sympatric in Thailand. The low level of sequence diversity in PocMSP-1 and PowMSP-1 among Thai isolates could stem from persistent low prevalence of these species, limiting the chance of outcrossing at this locus.
authors.affiliation: Molecular Biology of Malaria and Opportunistic Parasites Research Unit, Department of Parasitology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand. p.chaturong@gmail.com
authors.forename: Chaturong
authors.initials: C
authors.lastname: Putaporntip
authors.forename: Austin L
authors.initials: AL
authors.lastname: Hughes
authors.forename: Somchai
authors.initials: S
authors.lastname: Jongwutiwes
mesh_terms: D000293:Adolescent; D000328:Adult; D000595:Amino Acid Sequence; D002648:Child; D045303:Cytochromes b / Q000235:genetics; D005260:Female; D050259:Genes, Mitochondrial; D017125:Genes, Protozoan; D014644:Genetic Variation; D006801:Humans; D008297:Male; D020066:Merozoite Surface Protein 1 / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D041122:Plasmodium ovale / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D011110:Polymorphism, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013785:Thailand; D055815:Young Adult
chemical_list: D020066:Merozoite Surface Protein 1; D045303:Cytochromes b
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