Apollo: a sequencing-technology-independent, scalable and accurate assembly polishing algorithm.

A number of next-generation sequencing (NGS) technologies such as Roche/454, Illumina and AB SOLiD have recently become available. These technologies are capable of generating hundreds of thousands or tens of millions of short DNA sequence reads at a relatively low cost. These NGS technologies, now referred as second-generation sequencing (SGS) technologies, are being utilized for de novo sequencing, genome re-sequencing, and whole genome and transcriptome analysis. Now, new generation of sequencers, based on the 'next-next' or third-generation sequencing (TGS) technologies like the Single-Molecule Real-Time (SMRT™) Sequencer, Heliscope™ Single Molecule Sequencer, and the Ion Personal Genome Machine™ are becoming available that are capable of generating longer sequence reads in a shorter time and at even lower costs per instrument run. Ever declining sequencing costs and increased data output and sample throughput for NGS and TGS sequencing technologies enable the plant genomics and breeding community to undertake genotyping-by-sequencing (GBS). Data analysis, storage and management of large-scale second or TGS projects, however, are essential. This article provides an overview of different sequencing technologies with an emphasis on forthcoming TGS technologies and bioinformatics tools required for the latest evolution of DNA sequencing platforms.

The first generation sequencing technology based on the dideoxynucleotide (ddNTP) chain termination method proposed by Sanger was gradually eliminated due to its high cost, low sequencing read length and cumbersome process. The second generation of sequencing technology, called High-throughput sequencing (HTS), which was then developed, still has the problem of fixed read length. In recent years, the third generation sequencing technology represented by SMRT technology and Nanopore sequencing technology has gradually become popular. Compared with the previous two generations of sequencing technology, the most significant advantage of the third generation sequencing technology is its ability to carry out single molecule sequencing. In this process, the infinite length of nucleic acid sequence can be determined theoretically without the help of PCR amplification. This paper first introduces the basic principles, advantages and disadvantages of third-generation sequencing, and introduces in detail the CRISPR/Cas family-mediated SMRT technology and Nanopore sequencing technology in the third-generation sequencing technology. Finally, the research progress and prospects of the combination of the third generation sequencing technology and gene editing technology in the future are analyzed.

BackgroundThe advent of third-generation sequencing (TGS) technologies opens the door to improve genome assembly. Long reads are promising for enhancing the quality of fragmented draft assemblies constructed from next-generation sequencing (NGS) technologies. To date, a few algorithms that are capable of improving draft assemblies have released. There are SSPACE-LongRead, OPERA-LG, SMIS, npScarf, DBG2OLC, Unicycler, and LINKS. Hybrid assembly on large genomes remains challenging, however.ResultsWe develop a scalable and computationally efficient scaffolder, Long Reads Scaffolder (LRScaf, https://github.com/shingocat/lrscaf), that is capable of significantly boosting assembly contiguity using long reads. In this study, we summarise a comprehensive performance assessment for state-of-the-art scaffolders and LRScaf on seven organisms, i.e., E. coli, S. cerevisiae, A. thaliana, O. sativa, S. pennellii, Z. mays, and H. sapiens. LRScaf significantly improves the contiguity of draft assemblies, e.g., increasing the NGA50 value of CHM1 from 127.1 kbp to 9.4 Mbp using 20-fold coverage PacBio dataset and the NGA50 value of NA12878 from 115.3 kbp to 12.9 Mbp using 35-fold coverage Nanopore dataset. Besides, LRScaf generates the best contiguous NGA50 on A. thaliana, S. pennellii, Z. mays, and H. sapiens. Moreover, LRScaf has the shortest run time compared with other scaffolders, and the peak RAM of LRScaf remains practical for large genomes (e.g., 20.3 and 62.6 GB on CHM1 and NA12878, respectively).ConclusionsThe new algorithm, LRScaf, yields the best or, at least, moderate scaffold contiguity and accuracy in the shortest run time compared with other scaffolding algorithms. Furthermore, LRScaf provides a cost-effective way to improve contiguity of draft assemblies on large genomes.

BackgroundThe RNA virosphere's extensive diversity and its role in emerging infectious diseases underscore the importance of non-targeted sequencing for identifying unknown or rare pathogens, including co-infections. However, enriching low-abundance viral sequences in RNA metaviromics, particularly in the preparation of cDNA libraries and their compatibility with next-generation sequencing (NGS) and third-generation sequencing (TGS), remains challenging. Therefore, our objective is to develop and systematically assess a practical RNA metavirome methodology specifically tailored for the enrichment of low-abundance viral sequences within samples.MethodsWe developed the SMART-RNA-Metavirome platform, integrating SMART-9n library preparation with NGS and TGS technologies. Total RNA was extracted from two field-collected wild Aedes albopictus pools, along with one laboratory-infected Ae. albopictus pool harboring dengue virus (DENV). This RNA was subjected to reverse transcription using both this optimized protocol and random primer-based methods, followed by high-throughput sequencing on Illumina, Oxford Nanopore, and QitanTech Nanopore technologies. Welch's t-test was employed for comparative analysis of the subsequent RNA metavirome data, specifically to evaluate differences in viral species composition and abundance of viral reads between experimental groups. Furthermore, the effectiveness of this platform was systematically validated via RT-qPCR and SMART-RNA-Metavirome-based Oxford Nanopore sequencing across multiple sample types, including mosquito specimens from DENV-infected Ae. albopictus, serum samples from dengue patients and viral isolates of Japanese encephalitis virus (JEV) and Zika virus (ZIKV).ResultsThe SMART-RNA-Metavirome platform has been systematically validated to excel in enriching the composition and diversity of the RNA virome (P = 0.04), providing sufficient coverage for the complete reconstruction of viral genomes. When employed in the detection of DENV-infected Ae. albopictus, clinical serum samples, and viral isolates of JEV and ZIKV, this technique exhibits a robust correlation with RT-qPCR (r2 > 0.95). Notably, it demonstrates exceptional sensitivity, ensuring sufficient coverage even in samples of DENV-infected Ae. albopictus with a Ct-value of 35.3, attaining an impressive 99.88% genome coverage. Furthermore, this platform possesses the capability to identify virus species and determine their serotypes.ConclusionsIn our study, the SMART-RNA-Metavirome platform outperforms traditional methods, enriching RNA virome composition and diversity, enabling practical compatibility with both NGS and TGS technologies. It demonstrates significant proficiency in detecting both known and unknown arboviruses, even in low-titer samples such as those from wild mosquitoes and clinical sera. This platform facilitates comprehensive monitoring, risk assessment, and early warning of RNA virus transmissions, enhancing our understanding of RNA virome diversity and ecological patterns.Graphical abstractSupplementary InformationThe online version contains supplementary material available at 10.1186/s40249-025-01371-z.

Traditional methods for studying microbial communities have been limited due to difficulties in culturing and sequencing all microbial species. Recent advances in third-generation sequencing technologies, particularly PacBio’s high-fidelity (HiFi) sequencing, have significantly advanced metagenomics by providing accurate long-read sequences. This review explores the role of HiFi sequencing in overcoming the limitations of previous sequencing methods, including high error rates and fragmented assemblies. We discuss the benefits and applications of HiFi sequencing across various environments, such as the human gut and soil, which provides broader context for further exploration. Key studies are discussed to highlight HiFi sequencing’s ability to recover complete and coherent microbial genomes from complex microbiomes, showcasing its superior accuracy and continuity compared to other sequencing technologies. Additionally, we explore the potential applications of HiFi sequencing in quantitative microbial analysis, as well as the detection of single nucleotide variations (SNVs) and structural variations (SVs). PacBio HiFi sequencing is establishing a new benchmark in metagenomics, with the potential to significantly enhance our understanding of microbial ecology and drive forward advancements in both environmental and clinical applications.

BackgroundWith the continuous advances in third-generation sequencing technology and the increasing affordability of next-generation sequencing technology, sequencing data from different sequencing technology platforms is becoming more common. While numerous benchmarking studies have been conducted to compare variant-calling performance across different platforms and approaches, little attention has been paid to the potential of leveraging the strengths of different platforms to optimize overall performance, especially integrating Oxford Nanopore and Illumina sequencing data.ResultsWe investigated the impact of multi-platform data on the performance of variant calling through carefully designed experiments with a deep learning-based variant caller named Clair3-MP (Multi-Platform). Through our research, we not only demonstrated the capability of ONT-Illumina data for improved variant calling, but also identified the optimal scenarios for utilizing ONT-Illumina data. In addition, we revealed that the improvement in variant calling using ONT-Illumina data comes from an improvement in difficult genomic regions, such as the large low-complexity regions and segmental and collapse duplication regions. Moreover, Clair3-MP can incorporate reference genome stratification information to achieve a small but measurable improvement in variant calling. Clair3-MP is accessible as an open-source project at: https://github.com/HKU-BAL/Clair3-MP.ConclusionsThese insights have important implications for researchers and practitioners alike, providing valuable guidance for improving the reliability and efficiency of genomic analysis in diverse applications.

CpG methylation, a key epigenetic mark involved in gene regulation, development, and other biological processes, is commonly analyzed using Whole-Genome Bisulfite Sequencing (WGBS). However, bisulfite treatment causes significant DNA degradation. Enzymatic Methyl-seq (EM-seq) offers a short-read alternative that preserves DNA integrity but requires conversion steps, limiting its compatibility with downstream analyses. Third-generation sequencing technologies, such as Oxford Nanopore Technologies (ONT) and PacBio, enable direct detection of DNA modifications without altering the DNA, providing simultaneous genome and epigenome information. This work presents a comprehensive dataset combining long- and short-read sequencing data, including ONT, PacBio, Enzymatic Methyl-seq, and WGBS, for two agronomically relevant species: pig (Sus scrofa) and quail (Coturnix japonica). Data quality evaluation reveals high nucleotide quality scores for PacBio and short reads, robust alignment rates for long reads, and inter-method correlations in CpG methylation calling ranging from 0.76 to 0.99. This dataset is a valuable resource for training methylation callers and represents the first combined methylation dataset for these species, providing an essential benchmark for assessing emerging sequencing technologies.

Next-generation sequencing technologies have enabled many advances across diverse areas of biology, with many benefiting from increased sample size. Although the cost of running next-generation sequencing instruments has dropped substantially over time, the cost of sample preparation methods has lagged behind. To counter this, researchers have adapted library miniaturization protocols and large sample pools to maximize the number of samples that can be prepared by a certain amount of reagents and sequenced in a single run. However, due to high variability of sample quality, over and underrepresentation of samples in a sequencing run has become a major issue in high-throughput sequencing. This leads to misinterpretation of results due to increased noise, and additional time and cost rerunning underrepresented samples. To overcome this problem, we present a normalization method that uses shallow iSeq sequencing to accurately inform pooling volumes based on read distribution. This method is superior to the widely used fluorometry methods, which cannot specifically target adapter-ligated molecules that contribute to sequencing output. Our normalization method not only quantifies adapter-ligated molecules but also allows normalization of feature space; for example, we can normalize to reads of interest such as non-ribosomal reads. As a result, this normalization method improves the efficiency of high-throughput next-generation sequencing by reducing noise and producing higher average reads per sample with more even sequencing depth. IMPORTANCE High-throughput next generation sequencing (NGS) has significantly contributed to the field of genomics; however, further improvements can maximize the potential of this important tool. Uneven sequencing of samples in a multiplexed run is a common issue that leads to unexpected extra costs or low-quality data. To mitigate this problem, we introduce a normalization method based on read counts rather than library concentration. This method allows for an even distribution of features of interest across samples, improving the statistical power of data sets and preventing the financial loss associated with resequencing libraries. This method optimizes NGS, which already has huge importance across many areas of biology.

The investigation of plant genomes is of great importance for basic research and practical breeding. In 1977, F. Sanger proposed a DNA sequencing method, which allowed the complete sequences of a number of genomes to be determined. Then high-throughput and cost-effective next-generation/second-generation sequencing methods, producing up to billions of short reads, made it possible to sequence genomes of a significant number of species and provided a breakthrough in plant genetic studies. Finally, third-generation sequencing technologies allowed the determination of single-molecule sequences up to a million nucleotides in length, which is key for high-quality genome assemblies. An important task is to obtain a pan-genome, which includes an entire set of nucleotide sequences presented in various genotypes of the same species. The sequencing of plant genomes made it possible to assess intraspecific polymorphism, identify key genes influencing the formation of significant features, and develop molecular markers of economically valuable traits and this has become the basis for the development of marker-assisted and genomic selection. This review provides information on the latest advances in sequencing technologies and the assembly of plant genomes, as well as the opportunities that they open up for basic and applied works.

With the rapid advancement of sequencing technology, third-generation sequencing, particularly single-molecule real-time sequencing and nanopore sequencing, has opened new avenues for the precise prevention and control of genetic diseases. It offers distinct advantages, including long-read lengths, minimal requirement for extensive polymerase chain reaction amplification, and real-time sequencing capability. This narrative review summarizes and critically evaluates recent advances in the application and latest progress of third-generation sequencing in thalassemia. It focuses on the technical advantages and application status of this technology in detecting complex structural variations, large-scale carrier screening, prenatal diagnosis, and preimplantation genetic testing. The review further analyzes the considerable potential of this technology in improving diagnostic accuracy, shortening detection cycles, and reducing technical costs. Additionally, it discusses the challenges currently faced in data interpretation, standardized processes, and clinical translation. Finally, this review provides insights into future development directions, with the aim of providing new technical perspectives and a theoretical basis for optimizing the prevention and control strategies of thalassemia.

DNA exists biologically as a highly dynamic macromolecular complex subject to myriad chemical modifications that alter its physiological interpretation, yet most sequencing technologies only measure Watson-Crick base pairing interactions. Third-generation sequencing technologies can directly detect novel and modified bases, yet the difficulty and cost of training these techniques for each novel base has so far limited this potential. Here, we present a method based on barcoded split-pool synthesis to generate reference standard oligonucleotides allowing novel base sequencing. Using novel base detection, we perform multidimensional sequencing to retrieve information, both physiologically stored and experimentally encoded, from DNA, allowing us to characterize the preferential replication of deleterious mitochondrial genome mutations, the infection dynamics of a host-pathogen model, and the effect of chemotherapy on cancer cell DNA at the single molecule level. The low cost and experimental simplicity of this method make this approach widely accessible to the research community, enabling complex experimental interrogation across the biological sciences.

6.03 - Algorithms for Mapping High-Throughput DNA Sequences

Motivation: The explosion of next-generation sequencing data has spawned the design of new algorithms and software tools to provide efficient mapping for different read lengths and sequencing technologies. In particular, ABI's sequencer (SOLiD system) poses a big computational challenge with its capacity to produce very large amounts of data, and its unique strategy of encoding sequence data into color signals.Results: We present the mapping software, named PerM (Periodic Seed Mapping) that uses periodic spaced seeds to significantly improve mapping efficiency for large reference genomes when compared with state-of-the-art programs. The data structure in PerM requires only 4.5 bytes per base to index the human genome, allowing entire genomes to be loaded to memory, while multiple processors simultaneously map reads to the reference. Weight maximized periodic seeds offer full sensitivity for up to three mismatches and high sensitivity for four and five mismatches while minimizing the number random hits per query, significantly speeding up the running time. Such sensitivity makes PerM a valuable mapping tool for SOLiD and Solexa reads.Availability: http://code.google.com/p/perm/Contact: tingchen@usc.eduSupplementary information: Supplementary data are available at Bioinformatics online.

Recently, third-generation long-read sequencing technology has been increasingly applied to the detection of various blood group systems. Because of its long read length and use of single-molecule sequencing, it is capable of obtaining the sequences of blood group genes in their entirety as well as of distinguishing haplotypes. Therefore, here, we collected ABO blood group samples that were difficult to classify serologically and analysed the sequences of the coding regions of the ABO genes as well as the sequences upstream and downstream of the coding regions. Samples with ABO antigen typing and reverse serum typing discrepancies were screened in a total of 21 patients. All samples were subjected to serological testing and preliminary ABO genotyping (polymerase chain reaction with sequence-specific primers [PCR-SSP]), followed by single-molecule real-time (SMRT) sequencing to obtain complete ABO gene sequences. PCR sequence-based typing (PCR-SBT) was performed to validate the results. Of the 21 samples, 15 had common ABO types, and 6 had rare ABO subtypes. One new allele, ABO*B.NEW (c.861C>T), and one allelic base recombination event was identified. Forty-two haplotype sequences were obtained via SMRT sequencing with intronic single-nucleotide variants (SNVs) specific to the ABO allele, and all of the exon region sequences were consistent with the PCR-SBT results. SMRT sequencing is capable of accurately obtaining complete ABO gene sequences, distinguishing haplotypes and identifying allelic recombination.

Genome sequencing has been restricted to species with a small genome size. With the advent of second- and third-generation sequencing technologies, the potential to sequence genomes of all sizes is becoming a reality. As the field of whole genome sequencing has developed, there has been a growing appreciation of the need to better represent the major lineages of the plant tree of life, rather than just those that contain economically important taxa. We argue that as well as accounting for phylogenetic diversity when selecting species to analyse, in order to gain a comprehensive understanding of genome evolution, large-scale sequencing projects also need to reflect the diversity of genome sizes in plants. In this article we briefly outline evidence from the literature to support this view.