Evidence of Massive Horizontal Gene Transfer Between Humans and Plasmodium vivax

Abstract

The horizontal transfer of DNA between different organisms is a major force shaping the genomes of prokaryotes, but is considered to have a minor role in eukaryotes, with only a handful of known examples, mostly of limited size. The nucleotide databases of Plasmodium genomes were divided into small fragments and compared to human, as well as to other Plasmodium genomes. This computational approach revealed that the Plasmodium vivax genome is interlaced with multiple DNA fragments that were likely acquired via horizontal transfer from humans. Contamination is a major concern in such studies; moreover, it must be determined if the identified homologies might be due to chance. These reservations are supported by the fact that the identified homologous sequences were found to be predominantly within short contigs. Re-sequencing of candidate sites using distinct isolations of P. vivax genomic DNA showed deletions not found in the human genome, and with much greater similarity to the P. vivax than human genome. Moreover, the identified fragments were enriched for mRNA coding sequences and genes that are known to be functionally important for P. vivax, including nitric oxide synthase 1 (neuronal) adaptor and Interleukin-1 family, suggesting a functional role. These results are important for two reasons. First, a directional massive horizontal transfer of genetic material from humans to another eukaryote is shown for the first time. This sheds light on parasite evolution, co-adaptation and immune evasion. Second, the DNA found is enriched for Interleukin-1 family, which is known to be essential for malaria protection. This indicates a functional role and might serve to better understand how Plasmodium vivax and the immune system interact.