Biology subjects

Pevzner, P. A.

Publications and source records attributed to Pevzner, P. A..

14 recordsLinked to original sources

bioRxiv2022

SpLitteR: Diploid genome assembly using linked TELL-Seq reads and assembly graphs

BackgroundRecent advances in long-read sequencing technologies enabled accurate and contiguous de novo assemblies of large genomes and metagenomes. However, even long and accurate high-fidelity (HiFi) reads do not resolve repeats that are longer than the read lengths. This limitation negatively affects the contiguity of diploid genome assemblies since two haplomes share many long identical regions. To generate the telomere-to-telomere assemblies of diploid genomes, biologists now construct their HiFi-based phased assemblies and use additional experimental technologies to transform them into more contiguous diploid assemblies. The barcoded linked-reads, generated using an inexpensive TELL-Seq technology, provide an attractive way to bridge unresolved repeats in phased assemblies of diploid genomes. ResultsWe developed SpLitteR tool for diploid genome assembly using linked-reads and assembly graphs and benchmarked it against state-of-the-art linked-read scaffolders ARKS and SLR-superscaffolder using human HG002 genome and sheep gut microbiome datasets. The benchmark showed that SpLitteR scaffolding results in 1.5-fold increase in NGA50 compared to baseline LJA assembly and other scaffolders while introducing no additional misassemblies on the human dataset. ConclusionWe developed the SpLitteR tool for haplotype phasing and scaffolding in an assembly graph using barcoded linked-reads. We benchmarked SpLitteR on assembly graphs produced by various long-read assemblers and have shown how TELL-Seq reads facilitate phasing and scaffolding in these graphs. This benchmarking demonstrates that SpLitteR improves upon the state-of-the-art linked-read scaffolders in the accuracy and contiguity metrics. SpLitteR is implemented in C++ as a part of the freely available SPAdes package and is available at https://github.com/ablab/spades/releases/tag/splitter-preprint.

bioinformatics↗

bioRxiv2022

TandemAligner: a new parameter-free framework for fast sequence alignment

The recent advances in "complete genomics" revealed the previously inaccessible genomic regions (such as centromeres) and enabled analysis of their associations with diseases. However, analysis of variations in centromeres, immunoglobulin loci, and other extra-long tandem repeats (ETRs) faces an algorithmic bottleneck since there are currently no tools for accurate sequence comparison of ETRs. Counterintuitively, the classical alignment approaches, such as the Smith-Waterman algorithm, that work well for most sequences, fail to construct biologically adequate alignments of ETRs. This limitation was overlooked in previous studies since the ETR sequences across multiple genomes only became available in the last year. We present TandemAligner -- the first parameter-free sequence alignment algorithm that introduces a sequence-dependent alignment scoring that automatically changes for any pair of compared sequences. We apply TandemAligner to various human centromeres and primate immunoglobulin loci, arrive at the first accurate estimate of the mutation rates in human centromeres, and quantify the extremely high rate of large insertions/duplications in centromeres. This extremely high rate (that the standard alignment algorithms fail to uncover) suggests that centromeres represent the most rapidly evolving regions of the human genome with respect to their structural organization.

bioinformatics↗

bioRxiv2021

HORmon: automated annotation of human centromeres

Recent advances in long-read sequencing opened a possibility to address the long-standing questions about the architecture and evolution of human centromeres. They also emphasized the need for centromere annotation (partitioning human centromeres into monomers and higher-order repeats (HORs)). Even though there was a half-century-long series of semi-manual studies of centromere architecture, a rigorous centromere annotation algorithm is still lacking. Moreover, an automated centromere annotation is a prerequisite for studies of genetic diseases associated with centromeres, and evolutionary studies of centromeres across multiple species. Although the monomer decomposition (transforming a centromere into a monocentromere written in the monomer alphabet) and the HOR decomposition (representing a monocentromere in the alphabet of HORs) are currently viewed as two separate problems, we demonstrate that they should be integrated into a single framework in such a way that HOR (monomer) inference affects monomer (HOR) inference. We thus developed the HORmon algorithm that integrates the monomer/HOR inference and automatically generates the human monomers/HORs that are largely consistent with the previous semi-manual inference.

bioinformatics↗

bioRxiv2021

Revealing how variations in antibody repertoires correlate with vaccine responses

An important challenge in vaccine development is to figure out why a vaccine succeeds in some individuals and fails in others. Although antibody repertoires hold a key to answering this question, there have been very few personalized immunogenomics studies so far aimed at revealing how variations in immunoglobulin genes affect a vaccine response. We conducted an immunosequencing study of 204 calves vaccinated against bovine respiratory disease (BRD) with the goal to reveal variations in immunoglobulin genes and somatic hypermutations that impact the efficacy of vaccine response. Our study represents the largest longitudinal personalized immunogenomics study reported to date across all species, including humans. To analyze the generated dataset, we developed an algorithm for identifying variations of the immunoglobulin genes (as well as frequent somatic hypermutations) that affect various features of the antibody repertoire and titers of neutralizing antibodies. In contrast to relatively short human antibodies, cattle have a large fraction of ultralong antibodies that have opened new therapeutic opportunities. Our study revealed that ultralong antibodies are a key component of the immune response against the costliest disease of beef cattle in North America. The detected variants of the cattle immunoglobulin genes, which are implicated in the success/failure of the BRD vaccine, have the potential to direct the selection of individual cattle for ongoing breeding programs.

immunology↗

bioRxiv2021

Generation of lineage-resolved complete metagenome-assembled genomes by precision phasing

Microbial communities in many environments include distinct lineages of closely related organisms which have proved challenging to separate in metagenomic assembly, preventing generation of complete metagenome-assembled genomes (MAGs). The advent of long and accurate HiFi reads presents a possible means to address this challenge by generating complete MAGs for nearly all sufficiently abundant bacterial genomes in a microbial community. We present a metagenomic HiFi assembly of a complex microbial community from sheep fecal material that resulted in 428 high-quality MAGs from a single sample, the highest resolution achieved with metagenomic deconvolution to date. We applied a computational approach to separate distinct haplotype lineages and identified haplotypes of hundreds of variants across hundreds of kilobases of genomic sequence. Analysis of these haplotypes revealed 220 lineage-resolved complete MAGs, including 44 in single circular contigs, and demonstrated improvement in overall assembly compared to error-prone long reads. We report the characterization of multiple, closely-related microbes within a sample with potential to improve precision in assigning mobile genetic elements to host genomes within complex microbial communities.

microbiology↗

bioRxiv2020

Thousands of previously unknown phages discovered in whole-community human gut metagenomes

BackgroundDouble-stranded DNA bacteriophages (dsDNA phages) play pivotal roles in structuring human gut microbiomes; yet, the gut phageome is far from being fully characterized, and additional groups of phages, including highly abundant ones, continue to be discovered by metagenome mining. A multilevel framework for taxonomic classification of viruses was recently adopted, facilitating the classification of phages into evolutionary informative taxonomic units based on hallmark genes. Together with advanced approaches for sequence assembly and powerful methods of sequence analysis, this revised framework offers the opportunity to discover and classify unknown phage taxa in the human gut. ResultsA search of human gut metagenomes for circular contigs encoding phage hallmark genes resulted in the identification of 3,738 apparently complete phage genomes that represent 451 putative genera. Several of these phage genera are only distantly related to previously identified phages and are likely to found new families. Two of the candidate families, "Flandersviridae" and "Quimbyviridae", include some of the most common and abundant members of the human gut virome that infect Bacteroides, Parabacteroides and Prevotella. The third proposed family, "Gratiaviridae", consists of less abundant phages that are distantly related to the families Autographiviridae, Drexlerviridae and Chaseviridae. Analysis of CRISPR spacers indicates that phages of all three putative families infect bacteria of the phylum Bacteroidetes. Comparative genomic analysis of the three candidate phage families revealed features without precedent in phage genomes. Some "Quimbyviridae" phages possess Diversity-Generating Retroelements (DGRs) that generate hypervariable target genes nested within defense-related genes, whereas the previously known targets of phage-encoded DGRs are structural genes. Several "Flandersviridae" phages encode enzymes of the isoprenoid pathway, a lipid biosynthesis pathway that so far has not been known to be manipulated by phages. The "Gratiaviridae" phages encode a HipA-family protein kinase and glycosyltransferase, suggesting these phages modify the host cell wall, preventing superinfection by other phages. Hundreds of phages in these three and other families are shown to encode catalases and iron-sequestering enzymes that can be predicted to enhance cellular tolerance to reactive oxygen species. ConclusionsAnalysis of phage genomes identified in whole-community human gut metagenomes resulted in the delineation of at least three new candidate families of Caudovirales and revealed diverse putative mechanisms underlying phage-host interactions in the human gut. Addition of these phylogenetically classified, diverse and distinct phages to public databases will facilitate taxonomic decomposition and functional characterization of human gut viromes.

microbiology↗

bioRxiv2020

Unique genomic features of crAss-like phages, the dominant component of the human gut virome

CrAssphage is the most abundant virus identified in the human gut virome and the founding member of a large group of bacteriophages that infect bacteria of the phylum Bacteroidetes and have been discovered by metagenomics of both animal-associated and environmental habitats. By analysis of circular contigs from human gut microbiomes, we identified nearly 600 genomes of crAss-like phages. Phylogenetic analysis of conserved genes demonstrates the monophyly of crAss-like phages, which can be expected to become a new order of viruses, and of 5 distinct branches, likely, families within that order. Two of these putative families have not been identified previously. The phages in one of these groups have large genomes (145-192 kilobases) and contain an unprecedented high density of self-splicing introns and inteins. Many crAss-like phages encode suppressor tRNAs that enable readthrough of UGA or UAG stop-codons, mostly, in late phage genes, which could represent a distinct anti-defense strategy. Another putative anti-defense mechanism that might target an unknown defense system in Bacteroidetes inhibiting phage DNA replication involves multiple switches of the phage DNA polymerase type between A and B families. Thus, comparative genomic analysis of the expanded assemblage of crAss-like phages reveals several unusual features of genome architecture and expression as well as phage biology that were not apparent from the previous crAssphage analyses.

microbiology↗

bioRxiv2019

The String Decomposition Problem and its Applications to Centromere Assembly

Recent attempts to assemble long tandem repeats (such as multi-megabase long centromeres) faced the challenge of accurate translation of long error-prone reads from the nucleotide alphabet into the alphabet of repeat units. Centromeres represent a particularly complex type of nested tandem repeats, where each unit is itself a repeat formed by chromosome-specific monomers (a repeat within repeat). Given a set of monomers forming a specific centromere, translation of a read into monomers is modeled as the String Decomposition Problem, finding a concatenate of monomers with the highest-scoring sequence alignment to a given read. We developed a StringDecomposer algorithm for solving this problem, benchmarked it on the set of reads generated by the Telomere-to-Telomere consortium, and identified a novel (rare) monomer that extends the set of twelve X-chromosome specific monomers identified more than three decades ago. The accurate translation of each read into a monomer alphabet turns centromere assembly into a more tractable problem than the notoriously difficult problem of assembling centromeres in the nucleotide alphabet. Our identification of a novel monomer emphasizes the importance of careful identification of all (even rare) monomers for follow-up centromere assembly efforts.

bioinformatics↗

bioRxiv2019

TandemMapper and TandemQUAST: mapping long reads and assessing/improving assembly quality in extra-long tandem repeats

Extra-long tandem repeats (ETRs) are widespread in eukaryotic genomes and play an important role in fundamental cellular processes, such as chromosome segregation. Although emerging long-read technologies have enabled ETR assemblies, the accuracy of such assemblies is difficult to evaluate since there is no standard tool for their quality assessment. Moreover, since the mapping of long error-prone reads to ETR remains an open problem, it is not clear how to polish draft ETR assemblies. To address these problems, we developed the tandemMapper tool for mapping reads to ETRs and the tandemQUAST tool for polishing ETR assemblies and their quality assessment. We demonstrate that tandemQUAST not only reveals errors in and evaluates ETR assemblies, but also improves them. To illustrate how tandemMapper and tandemQUAST work, we apply them to recently generated assemblies of human centromeres.

bioinformatics↗

bioRxiv2019

centroFlye: Assembling Centromeres with Long Error-Prone Reads

Although variations in centromeres have been linked to cancer and infertility, centromeres still represent the \"dark matter of the human genome\" and remain an enigma for both biomedical and evolutionary studies. Since centromeres have withstood all previous attempts to develop an automated tool for their assembly and since their assembly using short reads is viewed as intractable, recent efforts attempted to manually assemble centromeres using long error-prone reads. We describe the centroFlye algorithm for centromere assembly using long error-prone reads, apply it for assembling the human X centromere, and use the constructed assembly to gain insights into centromere evolution. Our analysis reveals putative breakpoints in the previous manual reconstruction of the human X centromere and opens a possibility to automatically close the remaining multi-megabase gaps in the reference human genome.

bioinformatics↗

bioRxiv2019

IgEvolution: clonal analysis of antibody repertoires

Constructing antibody repertoires is an important error-correcting step in analyzing immunosequencing datasets that is important for reconstructing evolutionary (clonal) development of antibodies. However, the state-of-the-art repertoire construction tools typically miss low-abundance antibodies that often represent internal nodes in clonal trees and are crucially important for clonal tree reconstruction. Thus, although repertoire construction is a prerequisite for follow up clonal tree reconstruction, the existing repertoire reconstruction algorithms are not well suited for this task. Since clonal analysis has the potential to reveal errors in the constructed repertoires and contribute to constructing more accurate repertoires, we advocate a tree-guided construction of antibody repertoires that combines error correction and clonal reconstruction as interconnected (rather than independent) tasks. We developed the IgEvolution algorithm for simultaneous repertoire and clonal tree reconstruction and applied it for analyzing multiple immunosequencing datasets representing antigen-specific immune responses. We demonstrate that analysis of clonal trees reveals highly mutable positions that correlate with antigen-binding sites and light-chain contacts in crystallized antibody-antigen complexes. We further demonstrate that this analysis leads to a new approach for identifying complementarity determining regions (CDRs) in antibodies.

immunology↗

bioRxiv2019

De Novo Peptide Sequencing Reveals a Vast Cyclopeptidome in Human Gut and Other Environments

Cyclic and branch cyclic peptides (cyclopeptides) represent an important class of bioactive natural products that include many antibiotics and anti-tumor compounds. However, little is known about cyclopeptides in the human gut, despite the fact that humans are constantly exposed to them. To address this bottleneck, we developed the CycloNovo algorithm for de novo cyclopeptide sequencing that employs de Bruijn graphs, the workhorse of DNA sequencing algorithms. CycloNovo reconstructed many new cyclopeptides that we validated with transcriptome, metagenome, and genome mining analyses. Our benchmarking revealed a vast hidden cyclopeptidome in the human gut and other environments and suggested that CycloNovo offers a much-needed step-change for cyclopeptide discovery. Furthermore, CycloNovo revealed a wealth of anti-microbial cyclopeptides from food that survive the complete human gastrointestinal tract, raising the question of how these cyclopeptides might affect the human microbiome.\n\nSIGNIFICANCEThe golden age of antibiotics was followed by a decline in the pace of antibiotics discovery in the 1990s. The key prerequisite for the resurgence of antibiotics research is the development of a computational discovery pipeline for antibiotics sequencing. We describe such pipeline for cyclic and branch cyclic peptides (cyclopeptides) that represent an important class of bioactive natural products such as antibiotics and anti-tumor compounds. Our CycloNovo algorithm for cyclopeptide sequencing reconstructed many new cyclopeptides that we validated with transcriptome, metagenome, and genome mining analyses. CycloNovo revealed a wealth of anti-microbial cyclopeptides from food that survive the complete human gastrointestinal tract, raising the question of how these cyclopeptides might affect the human microbiome.

bioinformatics↗

bioRxiv2017

MetaRiPPquest: A Peptidogenomics Approach for the Discovery of Ribosomally Synthesized and Post-translationally Modified Peptides

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are an important class of natural products that include many antibiotics and a variety of other bioactive compounds. While recent breakthroughs in RiPP discovery raised the challenge of developing new algorithms for their analysis, peptidogenomic-based identification of RiPPs by combining genome/metagenome mining with analysis of tandem mass spectra remains an open problem. We present here MetaRiPPquest, a software tool for addressing this challenge that is compatible with large-scale screening platforms for natural product discovery. After searching millions of spectra in the Global Natural Products Social (GNPS) molecular networking infrastructure against just six genomic and metagenomic datasets, MetaRiPPquest identified 27 known and discovered 5 novel RiPP natural products.

bioinformatics↗

bioRxiv2017

The antibody repertoire of colorectal cancer

3Immunotherapy is becoming increasingly important in the fight against cancers, utilizing and manipulating the bodys immune response to treat tumors. Understanding the immune repertoire - the collection of immunological proteins - of treated and untreated cells is possible at the genomic, but technically difficult at the protein level. Standard protein databases do not include the highly divergent sequences of somatic rearranged immunoglobulin genes, and may lead to missed identifications in a mass spectrometry search. We introduce a novel proteogenomic approach, AbScan, to identify these highly variable antibody peptides, by developing a customized antibody database construction method using RNA-seq reads aligned to immunoglobulin (Ig) genes.\n\nAbScan starts by filtering transcript (RNA-seq) reads that match the template for Ig genes. The retained reads are used to construct a repertoire graph using the split de Bruijn graph: a graph structure that improves upon the standard de Bruijn graph to capture the high diversity of Ig genes in a compact manner. AbScan corrects for sequencing errors, and converts the graph to a format suitable for searching with MS/MS search tools. We used AbScan to create an antibody database from 90 RNA-seq colorectal tumor samples. Next, we used proteogenomics analysis to search MS/MS spectra of matched colorectal samples from the Clinical Proteomic Tumor Analysis Consortium (CPTAC) against the AbScan generated database. AbScan identified 1, 940 distinct antibody peptides. Correlating with previously identified Single Amino-Acid Variants (SAAVs) in the tumor samples, we identified 163 pairs (antibody peptide, SAAV) with significant co-occurrence pattern in the 90 samples. The presence of co-expressed antibody and mutated peptides was correlated with survival time of the individuals. Our results suggest that AbScan(https://github.com/csw407/AbScan.git) is an effective tool for a proteomic exploration of the immune response in cancers.\n\n\n\nO_TBL View this table:\norg.highwire.dtl.DTLVardef@62001corg.highwire.dtl.DTLVardef@1f542faorg.highwire.dtl.DTLVardef@10048d0org.highwire.dtl.DTLVardef@1ac5a75org.highwire.dtl.DTLVardef@66db0f_HPS_FORMAT_FIGEXP M_TBL C_TBL

bioinformatics↗