Selective whole-genome sequencing of Plasmodium parasites directly from blood samples by nanopore adaptive sampling

Abstract

ABSTRACTWhole-genome sequencing of Plasmodium is becoming an increasingly important tool for genomic surveillance of malaria. Due to the predominance of human DNA in a patient blood sample, time-consuming laboratory procedures are required to deplete human DNA or enrich Plasmodium DNA. Here, we investigated the potential of nanopore adaptive sampling to enrich Plasmodium falciparum reads while sequencing unenriched patient blood samples. To compare adaptive sampling versus regular sequencing on a MinION device, a dilution series consisting of 0%–84% P. falciparum DNA in human DNA was sequenced. Half of the flow cell channels were run in adaptive sampling mode, enriching for the P. falciparum reference genome, resulting in a three- to five-fold enrichment of P. falciparum bases in samples containing 0.1%–8.4% P. falciparum DNA. This finding was confirmed by sequencing three P. falciparum patient blood samples with common levels of parasitemia, that is, 0.1%, 0.2%, and 0.6% in adaptive mode. Their estimated enrichment was 5.8, 3.9, and 2.7, respectively, which was sufficient to cover at least 97% of the P. falciparum reference genome at a median depth of 5 (lowest parasitemia) or 355 (highest parasitemia). In all, 38 drug resistance loci were compared to Sanger sequencing results, showing high concordance, which suggests that the obtained sequencing data are of sufficient quality to address common clinical research questions for patients with parasitemias of 0.1% and higher. Overall, our results indicate that adaptive nanopore sequencing has the potential to replace more time-consuming Plasmodium enrichment protocols in the future.IMPORTANCEMalaria is caused by parasites of the genus Plasmodium, and reached a global disease burden of 247 million cases in 2021. To study drug resistance mutations and parasite population dynamics, whole-genome sequencing of patient blood samples is commonly performed. However, the predominance of human DNA in these samples imposes the need for time-consuming laboratory procedures to enrich Plasmodium DNA. We used the Oxford Nanopore Technologies’ adaptive sampling feature to circumvent this problem and enrich Plasmodium reads directly during the sequencing run. We demonstrate that adaptive nanopore sequencing efficiently enriches Plasmodium reads, which simplifies and shortens the timeline from blood collection to parasite sequencing. In addition, we show that the obtained data can be used for monitoring genetic markers, or to generate nearly complete genomes. Finally, owing to its inherent mobility, this technology can be easily applied on-site in endemic areas where patients would benefit the most from genomic surveillance.

Keywords

• Plasmodium falciparum
• nanopore sequencing
• adaptive sampling