From contigs towards chromosomes: automatic improvement of long read assemblies (ILRA)

Lineage-specific microbial protein prediction enables large-scale exploration of protein ecology within the human gut

Microbes use a range of genetic codes and gene structures, yet these are often ignored during metagenomic analysis. This causes spurious protein predictions, preventing functional assignment which limits our understanding of ecosystems. To resolve this, we developed a lineage-specific gene prediction approach that uses the correct genetic code based on the taxonomic assignment of genetic fragments, removes incomplete protein predictions, and optimises prediction of small proteins. Applied to 9634 metagenomes and 3594 genomes from the human gut, this approach increased the landscape of captured expressed microbial proteins by 78.9%, including previously hidden functional groups. Optimised small protein prediction captured 3,772,658 small protein clusters, which form an improved microbial protein catalogue of the human gut (MiProGut). To enable the ecological study of a protein's prevalence and association with host parameters, we developed InvestiGUT, a tool which integrates both the protein sequences and sample metadata. Accurate prediction of proteins is critical to providing a functional understanding of microbiomes, enhancing our ability to study interactions between microbes and hosts.

Comparison of nanopore with illumina whole genome assemblies of the Epstein-Barr virus in Burkitt lymphoma

Endemic Burkitt lymphoma (eBL) is one of the most prevalent cancer in children in sub-Saharan Africa, and while prior studies have found that Epstein-Barr virus (EBV) type and variation may alter the tumor driver genes necessary for tumor survival, the precise relationship between EBV variation and EBV-associated tumorigenesis remains unclear due to lack of scalable, cost-effective, viral whole-genome sequencing from tumor samples. This study introduces a rapid and cost-effective method of enriching, sequencing, and assembling accurate EBV genomes in BL tumor cell lines through a combination of selective whole genome amplification (sWGA) and subsequent 2-tube multiplex polymerase chain reaction along with long-read sequencing with a portable sequencer. The method was optimized across a range of parameters to yield a high percentage of EBV reads and sufficient coverage across the EBV genome except for large repeat regions. After optimization, we applied our method to sequence 18 cell lines and 3 patient tumors from fine needle biopsies and assembled them with median coverages of 99.62 and 99.68%, respectively. The assemblies showed high concordance (99.61% similarity) to available Illumina-based assemblies. The improved method and assembly pipeline will allow for better understanding of EBV variation in relation to BL and is applicable more broadly for translational research studies, especially useful for laboratories in Africa where eBL is most widespread.

Comparison of Nanopore with Illumina Whole Genome Assemblies of the Epstein-Barr Virus in Burkitt Lymphoma

Endemic Burkitt lymphoma (eBL) is one of the most prevalent cancer in children in sub-Saharan Africa, and while prior studies have found that Epstein-Barr virus (EBV) type and variation may alter the tumor driver genes necessary for tumor survival, the precise relationship between EBV variation and EBV-associated tumorigenesis remains unclear due to lack of scalable, cost-effective, viral whole-genome sequencing from tumor samples. This study introduces a rapid and cost-effective method of enriching, sequencing, and assembling accurate EBV genomes in BL tumor cell lines through a combination of selective whole genome amplification (sWGA) and subsequent 2-tube multiplex polymerase chain reaction along with long-read sequencing with a portable sequencer. The method was optimized across a range of parameters to yield a high percentage of EBV reads and sufficient coverage across the EBV genome except for large repeat regions. After optimization, we applied our method to sequence 18 cell lines and 3 patient tumors from fine needle biopsies and assembled them with median coverages of 99.62 and 99.68%, respectively. The assemblies showed high concordance (99.61% similarity) to available Illumina-based assemblies. The improved method and assembly pipeline will allow for better understanding of EBV variation in relation to BL and is applicable more broadly for translational research studies, especially useful for laboratories in Africa where eBL is most widespread.

Supersaturation mutagenesis reveals adaptive rewiring of essential genes among malaria parasites

Malaria parasites are highly divergent from model eukaryotes. Large-scale genome engineering methods effective in model organisms are frequently inapplicable, and systematic studies of gene function are few. We generated more than 175,000 transposon insertions in the Plasmodium knowlesi genome, averaging an insertion every 138 base pairs, and used this "supersaturation" mutagenesis to score essentiality for 98% of genes. The density of mutations allowed mapping of putative essential domains within genes, providing a completely new level of genome annotation for any Plasmodium species. Although gene essentiality was largely conserved across P. knowlesi, Plasmodium falciparum, and rodent malaria model Plasmodium berghei, a large number of shared genes are differentially essential, revealing species-specific adaptations. Our results indicated that Plasmodium essential gene evolution was conditionally linked to adaptive rewiring of metabolic networks for different hosts.

Genome drafts of Lotmaria passim strains C2 and C3 isolated from honey bees in Spain

Lotmaria passim is a highly prevalent parasite of honey bees. Herein is reported the draft genome sequences of L. passim C2 and C3 strains of 27.15 Mbp and 26.94 Mbp, respectively. The genomes were sequenced using Illumina MiSeq platform and will allow for further comparative and functional genomics studies.

Long-Read Sequencing and De Novo Genome Assembly Pipeline of Two Plasmodium falciparum Clones (Pf3D7, PfW2) Using Only the PromethION Sequencer from Oxford Nanopore Technologies without Whole-Genome Amplification

Antimalarial drug resistance has become a real public health problem despite WHO measures. New sequencing technologies make it possible to investigate genomic variations associated with resistant phenotypes at the genome-wide scale. Based on the use of hemisynthetic nanopores, the PromethION technology from Oxford Nanopore Technologies can produce long-read sequences, in contrast to previous short-read technologies used as the gold standard to sequence Plasmodium. Two clones of P. falciparum (Pf3D7 and PfW2) were sequenced in long-read using the PromethION sequencer from Oxford Nanopore Technologies without genomic amplification. This made it possible to create a processing analysis pipeline for human Plasmodium with ONT Fastq only. De novo assembly revealed N50 lengths of 18,488 kb and 17,502 kb for the Pf3D7 and PfW2, respectively. The genome size was estimated at 23,235,407 base pairs for the Pf3D7 clone and 21,712,038 base pairs for the PfW2 clone. The average genome coverage depth was estimated at 787X and 653X for the Pf3D7 and PfW2 clones, respectively. This study proposes an assembly processing pipeline for the human Plasmodium genome using software adapted to large ONT data and the high AT percentage of Plasmodium. This search provides all the parameters which were optimized for use with the software selected in the pipeline.

Benchmarking multi-platform sequencing technologies for human genome assembly

Genome assembly is a computational technique that involves piecing together deoxyribonucleic acid (DNA) fragments generated by sequencing technologies to create a comprehensive and precise representation of the entire genome. Generating a high-quality human reference genome is a crucial prerequisite for comprehending human biology, and it is also vital for downstream genomic variation analysis. Many efforts have been made over the past few decades to create a complete and gapless reference genome for humans by using a diverse range of advanced sequencing technologies. Several available tools are aimed at enhancing the quality of haploid and diploid human genome assemblies, which include contig assembly, polishing of contig errors, scaffolding and variant phasing. Selecting the appropriate tools and technologies remains a daunting task despite several studies have investigated the pros and cons of different assembly strategies. The goal of this paper was to benchmark various strategies for human genome assembly by combining sequencing technologies and tools on two publicly available samples (NA12878 and NA24385) from Genome in a Bottle. We then compared their performances in terms of continuity, accuracy, completeness, variant calling and phasing. We observed that PacBio HiFi long-reads are the optimal choice for generating an assembly with low base errors. On the other hand, we were able to produce the most continuous contigs with Oxford Nanopore long-reads, but they may require further polishing to improve on quality. We recommend using short-reads rather than long-reads themselves to improve the base accuracy of contigs from Oxford Nanopore long-reads. Hi-C is the best choice for chromosome-level scaffolding because it can capture the longest-range DNA connectedness compared to 10× linked-reads and Bionano optical maps. However, a combination of multiple technologies can be used to further improve the quality and completeness of genome assembly. For diploid assembly, hifiasm is the best tool for human diploid genome assembly using PacBio HiFi and Hi-C data. Looking to the future, we expect that further advancements in human diploid assemblers will leverage the power of PacBio HiFi reads and other technologies with long-range DNA connectedness to enable the generation of high-quality, chromosome-level and haplotype-resolved human genome assemblies.

Highly accurate genome assembly of an improved high-yielding silkworm strain, Nichi01

The silkworm (Bombyx mori) is an important lepidopteran model insect and an industrial domestic animal traditionally used for silk production. Here, we report the genome assembly of an improved Japanese strain Nichi01, in which the cocoon yield is comparable to that of commercial silkworm strains. The integration of PacBio Sequel II long-read and ddRAD-seq-based high-density genetic linkage map achieved the highest quality genome assembly of silkworms to date; 22 of the 28 pseudomolecules contained telomeric repeats at both ends, and only four gaps were present in the assembly. A total of 452 Mbp of the assembly with an N50 of 16.614 Mbp covered 99.3% of the complete orthologs of the lepidopteran core genes. Although the genome sequence of Nichi01 and that of the previously reported low-yielding tropical strain p50T assured their accuracy in most regions, we corrected several regions, misassembled in p50T, in our assembly. A total of 18,397 proteins were predicted using over 95 Gb of mRNA-seq derived from 10 different organs, covering 96.9% of the complete orthologs of the lepidopteran core genes. The final assembly and annotation files are available in KAIKObase (https://kaikobase.dna.affrc.go.jp/index.html) along with a genome browser and BLAST searching service, which would facilitate further studies and the breeding of silkworms and other insects.