Project description:Modest target sequencing yield improvements using Nanopore adaptive sampling to reduce human DNA contamination from clinical tissue samples
Project description:Technological and computational advancements in the fields of genomics and bioinformatics are providing exciting new opportunities for pathogen discovery and genomic surveillance. In particular, single-molecule nucleotide sequence data originating from Oxford Nanopore Technologies (ONT) sequencing platforms can be bioinformatically leveraged, in real-time, for enhanced biosurveillance of a vast array of zoonoses. The recently released nanopore adaptive sampling (NAS) strategy facilitates immediate mapping of individual nucleotide molecules to a given reference as each molecule is being sequenced. User-defined thresholds then allow for the retention or rejection of specific molecules, informed by the real-time reference mapping results, as they are physically passing through a given sequencing nanopore. Here, we show how NAS can be used to selectively sequence DNA of multiple bacterial tick-borne pathogens circulating in wild populations of the blacklegged tick vector, Ixodes scapularis.
Project description:Bacterial plasmids play a major role in the spread of antibiotic resistance genes. However, their characterization via DNA sequencing suffers from the low abundance of plasmid DNA in those samples. Although sample preparation methods can enrich the proportion of plasmid DNA before sequencing, these methods are expensive and laborious, and they might introduce a bias by enriching only for specific plasmid DNA sequences. Nanopore adaptive sampling could overcome these issues by rejecting uninteresting DNA molecules during the sequencing process. In this study, we assess the application of adaptive sampling for the enrichment of low-abundant plasmids in known bacterial isolates using two different adaptive sampling tools. We show that a significant enrichment can be achieved even on expired flow cells. By applying adaptive sampling, we also improve the quality of de novo plasmid assemblies and reduce the sequencing time. However, our experiments also highlight issues with adaptive sampling if target and non-target sequences span similar regions.ImportanceAntimicrobial resistance causes millions of deaths every year. Mobile genetic elements like bacterial plasmids are key drivers for the dissemination of antimicrobial resistance genes. This makes the characterization of plasmids via DNA sequencing an important tool for clinical microbiologists. Since plasmids are often underrepresented in bacterial samples, plasmid sequencing can be challenging and laborious. To accelerate the sequencing process, we evaluate nanopore adaptive sampling as an in silico method for the enrichment of low-abundant plasmids. Our results show the potential of this cost-efficient method for future plasmid research but also indicate issues that arise from using reference sequences.
Project description:DNA sequencing using nanopore technologies with the affordable MinION device is useful for the identification and characterization of structural variants, long haplotypes, sequencing of repetitive regions and identification of epigenetic modifications. The main limitation of this approach is the low coverage obtained, which might be avoided by adaptive sampling, a computationally controlled method of enrichment for targeted genomic regions. This study dissects the factors involved in the enrichment by adaptive sampling of a panel of 18 human genome regions containing 20 genes implicated in breast cancer sequenced in 16 patients with familial breast cancer negative for NGS screening. An average coverage of 2.0x was obtained for the whole genome and 5.1x for selected regions. Sequencing time was the main factor improving coverage. The selection of long reads (>1 Kb) did not improve the enrichment. The length of the selected region, which in our study ranged from 126 to 565 Kb, did not play a significant role in enrichment. However, the region containing PMS2 showed significantly lower coverage, which could be explained by the high number of PMS2 pseudogenes (N = 14), which were also enriched. Our study shows new evidence of enrichment obtained by adaptive sampling in a panel of genomic regions and shows parameters, the relevance of sequencing time and the role of pseudogenes, that improve the enrichment yield with no library reloading or GPU use, data useful for a more efficient application of this procedure in future studies.
Project description:Insect symbionts can alter their host phenotype and their effects can range from beneficial to pathogenic. Moreover, many insects exhibit co-infections, making their study more challenging. Less than 1% of insect species have high-quality referenced genomes available and fewer still also have their symbionts sequenced. Two methods are commonly used to sequence symbionts: whole-genome sequencing to concomitantly capture the host and bacterial genomes, or isolation of the symbiont's genome before sequencing. These methods are limited when dealing with rare or poorly characterized symbionts. Long-read technology is an important tool to generate high-quality genomes as they can overcome high levels of heterozygosity, repeat content, and transposable elements that confound short-read methods. Oxford Nanopore (ONT) adaptive sampling allows a sequencing instrument to select or reject sequences in real time. We describe a method based on ONT adaptive sampling (subtractive) approach that readily permitted the sequencing of the complete genomes of mitochondria, Buchnera and its plasmids (pLeu, pTrp), and Wolbachia genomes in two aphid species, Aphis glycines and Pentalonia nigronervosa. Adaptive sampling is able to retrieve organelles such as mitochondria and symbionts that have high representation in their hosts such as Buchnera and Wolbachia, but is less successful at retrieving symbionts in low concentrations.