Divergent pattern of genomic variation in Plasmodium falciparum and P. vivax [version 1; peer review: 2 approved with reservations]

The two main species causing malaria in humans, Plasmodium falciparum and P. vivax, differ significantly from each other in their evolutionary response to common drugs, but the reasons for this are not clear. Here we utilized the recently available large-scale genome sequencing data from these parasites and compared the pattern of single nucleotide polymorphisms, which may be related to these differences. We found that there was a five-fold higher preference for AT nucleotides compared to GC nucleotides at synonymous single nucleotide polymorphism sites in P. vivax. The preference for AT nucleotides was also present at non-synonymous sites, which lead to amino acid changes favouring those with codons of higher AT content. The substitution bias was also present at low and moderately conserved amino acid positions, but not at highly conserved positions. No marked bias was found at synonymous and non-synonymous sites in P. falciparum. The difference in the substitution bias between P. falciparum and P. vivax found in the present study may possibly contribute to their divergent evolutionary response to similar drug pressures.