Biology subjects

Dillon, K. C.

Publications and source records attributed to Dillon, K. C..

4 recordsLinked to original sources

bioRxiv2026

Optimizing genome assembly, chromosome synteny, and genetic variant discovery from Oxford Nanopore sequences of Dermacentor reticulatus ticks

Generating high-quality genome assemblies for small animals with large genomes is complex due to their small body size, DNA contamination, and repetitive elements. Ticks exemplify these complexities, while also being a global health threat to humans, domestic animals, and wildlife. Advances in long-read sequencing platforms now make it feasible to obtain large amounts of raw sequence data from individual specimens, but challenges remain. Key genome workflow challenges include error correction, assembly, transposable element annotation, and chromosome assignment and synteny. Here we examine three individual Dermacentor reticulatus ticks using deep Oxford Nanopore sequencing. Comparing and contrasting bioinformatic tools for raw read and assembly manipulation allows us to identify the parameters that provide a high-quality haploid genome assembly among 38 assemblies. We find Dorado error corrected raw read data from approximately two flow cells are needed, but limiting assembly coverage to 40x produces the highest quality assemblies. Then we examined the effects of optimal workflow parameters on downstream analyses of gene synteny and manual transposable element annotation of the three tick assemblies in comparison to an independent assembly of a fourth D. reticulatus individual from a different country. Gene synteny analysis allows chromosome assignment of scaffolds and transposable element identification was improved markedly with manual curation. Finally, we compared the genetic variation of D. reticulatus across two populations and found similar genetic diversity. Our study provides a clear workflow to obtain high-quality assemblies from Oxford Nanopore sequences and genetic characterization of a species with a large, complex, and repetitive genome.

genomics↗

bioRxiv2025

Tick Genome Assemblies: Overcoming biological limitations through advances in sequencing and assembly

Ticks are blood-feeding arthropods with approximately 1,000 species, however, only 24 species currently have a genome assembly. These genome assemblies are important resources to advance tick biology and control of tick-associated diseases. Generating tick genome assemblies is challenging due to their small body size (low DNA input), DNA contamination (from microbiota and host bloodmeals), large genome size (on average 2.4 Gbp for hard ticks), and abundant transposable elements (at least 68% of the assembly for Ixodes species). Advances in sequencing technologies have driven an increasing number of tick assemblies from 2011 to 2025. We characterize and assess the 54 tick genome assemblies within public genome databases using QUAST-LG and BUSCO compleasm. Then we evaluate the impact of biological source material and sequencing platforms on these tick genome assemblies. From the 54 tick assemblies, we identify 34 high-quality assemblies from 21 species that are suitable for downstream analyses. We recommend future tick genome assemblies use long-read sequencing platforms and Hi-C scaffolding to improve genomic resources for these unique blood-feeding parasites.

genomics↗

bioRxiv2024

Comparison of three tiled amplicon sequencing approaches for SARS-CoV-2 variant detection from wastewater

During the COVID-19 pandemic, the detection and sequencing of SARS-CoV-2 from wastewater proved to be a valuable tool in assessing trends at the community level. Several whole genome enrichment methods have been proposed for sequencing SARS-CoV-2 from the mixed wastewater community, but there is little consensus on the most appropriate sequencing methods for variant detection or abundance estimations. Few studies have elucidated the errors associated with these methods or have established minimum sequencing requirements for correct interpretation of the results. To address these needs, we systematically assessed the efficacy of three tiled amplicon enrichment methods (Freed/Midnight, ARTIC V4, NEB VarSkip) for whole genome sequencing of SARS-CoV-2 variants using mock wastewater communities with variants at known proportions. We found the ARTIC V4 approach yielded the most accurate results for variant identification and variant abundance estimation, followed by the NEB VarSkip approach. Conversely, the NEB VarSkip method obtained the highest genomic coverage, with the ARTIC V4 method achieving the second highest coverage. Finally, we determined that the Freed/Midnight library preparation methods are not well-suited for use with short read sequencing. Based on the present results, the ARTIC V4 workflow appears to be the most robust and cost-effective approach for monitoring circulating SARS-CoV-2 variants with wastewater surveillance. IMPORTANCEThis work is informative for practitioners of wastewater-based epidemiology. Here, we detail a systematic comparison of three tiled amplicon sequencing approaches for enrichment of SARS-CoV-2 variants from wastewater. Using mock communities of known variant composition, we validate the analysis methods previously published by Baaijens et al. in Genome Biology (2022) for estimating variant abundance from wastewater using an RNAseq pipeline, kallisto. We provide recommendations for minimum sequencing requirements for accurate abundance estimates of SARS-CoV-2 variants in wastewater. The sequences generated from the mock communities have been uploaded to NCBIs Sequence Read Archive and will be useful to other practitioners seeking to validate their sequencing methods or bioinformatic pipelines.

genomics↗

bioRxiv2024

The repetitive genome of the Ixodes ricinus tick reveals transposable elements have driven genome evolution in ticks

Ticks are obligate blood-feeding parasites associated with a huge diversity of diseases globally. The hard tick Ixodes ricinus is the key vector of Lyme borreliosis and tick-borne encephalitis in Western Eurasia. Ixodes ticks have large and repetitive genomes that are not yet well characterized. Here we generate two high-quality I. ricinus genome assemblies, with haploid genome sizes of approximately 2.15 Gbp. We find transposable elements comprise at least 69% of the two I. ricinus genomes, amongst the highest proportions found in animals. The transposable elements in ticks are highly diverse and novel, so we constructed a repeat library for ticks using our I. ricinus genomes and the genome of I. scapularis, another major tick vector of Lyme borreliosis. To understand the impact of transposable elements on tick genomes we compared their accumulation in the two Ixodes sister species. We find transposable elements in these two species to be drivers of genome evolution in ticks. The I. ricinus genome assemblies and our tick repeat library will be valuable resources for biological insights into this important ectoparasite. Our findings highlight that further research into the impact of transposable elements on the genomes of blood-feeding parasites is required.

genomics↗