Polishing De Novo Nanopore Assemblies of Bacteria and Eukaryotes With FMLRC2

Transduction of Lentiviral Vectors and ADORA3 in HEK293T Cells Modulated in Gene Expression and Alternative Splicing

For steady transgenic expression, lentiviral vector-mediated gene delivery is a commonly used technique. One question that needs to be explored is how external lentiviral vectors and overexpressed genes perturb cellular homeostasis, potentially altering transcriptional networks. In this study, two Human Embryonic Kidney 293T (HEK293T)-derived cell lines were established via lentiviral transduction, one overexpressing green fluorescent protein (GFP) and the other co-overexpressing GFP and ADORA3 following puromycin selection to ensure stable genomic integration. Genes with differentially transcript utilization (gDTUs) and differentially expressed genes (DEGs) across cell lines were identified after short-read and long-read RNA-seq. Only 31 genes were discovered to have changed in expression when GFP was expressed, although hundreds of genes showed variations in transcript use. In contrast, even when co-overexpression of GFP and ADORA3 alters the expression of more than 1000 genes, there are still less than 1000 gDTUs. Moreover, DEGs linked to ADORA3 overexpression play a major role in RNA splicing, whereas gDTUs are highly linked to a number of malignancies and the molecular mechanisms that underlie them. For the analysis of gene expression data from stable cell lines derived from HEK293T, our findings provide important insights into changes in gene expression and alternative splicing.

Comparative Genomics Points to Ecological Drivers of Genomic Divergence Among Intertidal Limpets

Comparative genomic studies of closely related taxa are important for our understanding of the causes of divergence on a changing Earth. This being said, the genomic resources available for marine intertidal molluscs are limited and currently, there are few publicly available high-quality annotated genomes for intertidal species and for molluscs in general. Here we report transcriptome assemblies for six species of Patellogastropoda and genome assemblies and annotations for three of these species (Scurria scurra, Scurria viridula and Scurria zebrina). Comparative analysis using these genomic resources suggest that and recently diverging lineages (10-20 Mya) have experienced similar amounts of contractions and expansions but across different gene families. Furthermore, differences among recently diverged species are reflected in variation in the amount of coding and noncoding material in genomes, such as amount of repetitive elements and lengths of transcripts and introns and exons. Additionally, functional ontologies of species-specific and duplicated genes together with demographic inference support the finding that recent divergence among members of the genus Scurria aligns with their unique ecological characteristics. Overall, the resources presented here will be valuable for future studies of adaptation in molluscs and in intertidal habitats as a whole.

Kastor: a reference-based comparative approach for assessment and correction of gene-fragmenting errors in long-read assemblies of small genomes

Long read sequencing technologies provide an efficient approach to generating highly contiguous and informative assemblies. However, higher relative error rates can introduce frameshifts and premature stop codons that pseudogenize genes, hindering downstream analyses. We developed a software tool that detects gene-fragmenting errors in draft assemblies of small genomes through comparison with a curated set of reference genome sequences and raw read information. In our presented example, detected errors represent less than 0.05% of the genome, but when corrected reduced the rate of pseudogenes from 23.3 to 5.6% in example long read assemblies, comparable to the rate of pseudogenes in short read assemblies. We demonstrate that this software can detect assembly errors in long read assemblies generated from small genomes and correct them to de-fragment genes.

The mitochondrial genome of Carex pseudochinensis H. Lév. & Vaniot, an endemic sedge in Korea

Carex pseudochinensis H. Lév. & Vaniot is an endemic species in Korea and is included in the clade of section Paludosae in the recent classification system. We present the complete mitochondrial genome sequence of C. pseudochinensis based on the POLAP pipeline with both long- and short-read sequences. The mitochondrial genome is 997,628 bp in length, containing two large regions of 536.94 and 419.04 kbp, respectively, and a pair of direct repeat regions of about 20.25 kbp. The genome contains 57 genes, including 31 protein-coding genes, 20 tRNAs, and 6 rRNAs. Phylogenetic analysis based on mitochondrial proteomes, including those from ten species of related taxa, confirmed a close phylogenetic relationship between C. breviculmis and C. pseudochinensis.

Simple, reference-independent assessment to empirically guide correction and polishing of hybrid microbial community metagenomic assembly

Hybrid metagenomic assembly of microbial communities, leveraging both long- and short-read sequencing technologies, is becoming an increasingly accessible approach, yet its widespread application faces several challenges. High-quality references may not be available for assembly accuracy comparisons common for benchmarking, and certain aspects of hybrid assembly may benefit from dataset-dependent, empiric guidance rather than the application of a uniform approach. In this study, several simple, reference-free characteristics-particularly coding gene content and read recruitment profiles-were hypothesized to be reliable indicators of assembly quality improvement during iterative error-fixing processes. These characteristics were compared to reference-dependent genome- and gene-centric analyses common for microbial community metagenomic studies. Two laboratory-scale bioreactors were sequenced with short- and long-read platforms, and assembled with commonly used software packages. Following long read assembly, long read correction and short read polishing were iterated up to ten times to resolve errors. These iterative processes were shown to have a substantial effect on gene- and genome-centric community compositions. Simple, reference-free assembly characteristics, specifically changes in gene fragmentation and short read recruitment, were robustly correlated with advanced analyses common in published comparative studies, and therefore are suitable proxies for hybrid metagenome assembly quality to simplify the identification of the optimal number of correction and polishing iterations. As hybrid metagenomic sequencing approaches will likely remain relevant due to the low added cost of short-read sequencing for differential coverage binning or the ability to access lower abundance community members, it is imperative that users are equipped to estimate assembly quality prior to downstream analyses.

Comparative genomics of Metarhizium brunneum strains V275 and ARSEF 4556: unraveling intraspecies diversity

Entomopathogenic fungi belonging to the Order Hypocreales are renowned for their ability to infect and kill insect hosts, while their endophytic mode of life and the beneficial rhizosphere effects on plant hosts have only been recently recognized. Understanding the molecular mechanisms underlying their different lifestyles could optimize their potential as both biocontrol and biofertilizer agents, as well as the wider appreciation of niche plasticity in fungal ecology. This study describes the comprehensive whole genome sequencing and analysis of one of the most effective entomopathogenic and endophytic EPF strains, Metarhizium brunneum V275 (commercially known as Lalguard Met52), achieved through Nanopore and Illumina reads. Comparative genomics for exploring intraspecies variability and analyses of key gene sets were conducted with a second effective EPF strain, M. brunneum ARSEF 4556. The search for strain- or species-specific genes was extended to M. brunneum strain ARSEF 3297 and other species of genus Metarhizium, to identify molecular mechanisms and putative key genome adaptations associated with mode of life differences. Genome size differed significantly, with M. brunneum V275 having the largest genome amongst M. brunneum strains sequenced to date. Genome analyses revealed an abundance of plant-degrading enzymes, plant colonization-associated genes, and intriguing intraspecies variations regarding their predicted secondary metabolic compounds and the number and localization of Transposable Elements. The potential significance of the differences found between closely related endophytic and entomopathogenic fungi, regarding plant growth-promoting and entomopathogenic abilities, are discussed, enhancing our understanding of their diverse functionalities and putative applications in agriculture and ecology.

Genome assembly in the telomere-to-telomere era

Genome sequences largely determine the biology and encode the history of an organism, and de novo assembly - the process of reconstructing the genome sequence of an organism from sequencing reads - has been a central problem in bioinformatics for four decades. Until recently, genomes were typically assembled into fragments of a few megabases at best, but now technological advances in long-read sequencing enable the near-complete assembly of each chromosome - also known as telomere-to-telomere assembly - for many organisms. Here, we review recent progress on assembly algorithms and protocols, with a focus on how to derive near-telomere-to-telomere assemblies. We also discuss the additional developments that will be required to resolve remaining assembly gaps and to assemble non-diploid genomes.

Utilizing Deep Neural Networks to Fill Gaps in Small Genomes

With the widespread adoption of next-generation sequencing technologies, the speed and convenience of genome sequencing have significantly improved, and many biological genomes have been sequenced. However, during the assembly of small genomes, we still face a series of challenges, including repetitive fragments, inverted repeats, low sequencing coverage, and the limitations of sequencing technologies. These challenges lead to unknown gaps in small genomes, hindering complete genome assembly. Although there are many existing assembly software options, they do not fully utilize the potential of artificial intelligence technologies, resulting in limited improvement in gap filling. Here, we propose a novel method, DLGapCloser, based on deep learning, aimed at assisting traditional tools in further filling gaps in small genomes. Firstly, we created four datasets based on the original genomes of Saccharomyces cerevisiae, Schizosaccharomyces pombe, Neurospora crassa, and Micromonas pusilla. To further extract effective information from the gene sequences, we also added homologous genomes to enrich the datasets. Secondly, we proposed the DGCNet model, which effectively extracts features and learns context from sequences flanking gaps. Addressing issues with early pruning and high memory usage in the Beam Search algorithm, we developed a new prediction algorithm, Wave-Beam Search. This algorithm alternates between expansion and contraction phases, enhancing efficiency and accuracy. Experimental results showed that the Wave-Beam Search algorithm improved the gap-filling performance of assembly tools by 7.35%, 28.57%, 42.85%, and 8.33% on the original results. Finally, we established new gap-filling standards and created and implemented a novel evaluation method. Validation on the genomes of Saccharomyces cerevisiae, Schizosaccharomyces pombe, Neurospora crassa, and Micromonas pusilla showed that DLGapCloser increased the number of filled gaps by 8.05%, 15.3%, 1.4%, and 7% compared to traditional assembly tools.

How low can you go? Short-read polishing of Oxford Nanopore bacterial genome assemblies

It is now possible to assemble near-perfect bacterial genomes using Oxford Nanopore Technologies (ONT) long reads, but short-read polishing is usually required for perfection. However, the effect of short-read depth on polishing performance is not well understood. Here, we introduce Pypolca (with default and careful parameters) and Polypolish v0.6.0 (with a new careful parameter). We then show that: (1) all polishers other than Pypolca-careful, Polypolish-default and Polypolish-careful commonly introduce false-positive errors at low read depth; (2) most of the benefit of short-read polishing occurs by 25× depth; (3) Polypolish-careful almost never introduces false-positive errors at any depth; and (4) Pypolca-careful is the single most effective polisher. Overall, we recommend the following polishing strategies: Polypolish-careful alone when depth is very low (<5×), Polypolish-careful and Pypolca-careful when depth is low (5-25×), and Polypolish-default and Pypolca-careful when depth is sufficient (>25×).

Complete genome sequence of Pseudomonas entomophila strain TVIN-A01

The complete genome sequence of Pseudomonas entomophila strain TVIN-A01 is reported in this manuscript. It is a commonly used laboratory strain of Pseudomonas entomophila known to infect insects and, hence, often studied in host-pathogen interactions. Oxford Nanopore sequencing and Illumina sequencing were performed to assemble the genome completely.

Chromosome-level genome assemblies of Nicotiana tabacum, Nicotiana sylvestris, and Nicotiana tomentosiformis

The Solanaceae species Nicotiana tabacum, an economically important crop plant cultivated worldwide, is an allotetraploid species that appeared about 200,000 years ago as the result of the hybridization of diploid ancestors of Nicotiana sylvestris and Nicotiana tomentosiformis. The previously published genome assemblies for these three species relied primarily on short-reads, and the obtained pseudochromosomes only partially covered the genomes. In this study, we generated annotated de novo chromosome-level genomes of N. tabacum, N. sylvestris, and N. tomentosiformis, which contain 3.99 Gb, 2.32 Gb, and 1.74 Gb, respectively of sequence data, with 97.6%, 99.5%, and 95.9% aligned in chromosomes, and represent 99.2%, 98.3%, and 98.5% of the near-universal single-copy orthologs Solanaceae genes. The completion levels of these chromosome-level genomes for N. tabacum, N. sylvestris, and N. tomentosiformis are comparable to other reference Solanaceae genomes, enabling more efficient synteny-based cross-species research.

Ubiquitous genome streamlined Acidobacteriota in freshwater environments

Acidobacteriota are abundant in soil, peatlands, and sediments, but their ecology in freshwater environments remains understudied. UBA12189, an Acidobacteriota genus, is an uncultivated, genome-streamlined lineage with a small genome size found in aquatic environments where detailed genomic analyses are lacking. Here, we analyzed 66 MAGs of UBA12189 (including one complete genome) from freshwater lakes and rivers in Europe, North America, and Asia. UBA12189 has small genome sizes (<1.4 Mbp), low GC content, and a highly diverse pangenome. In freshwater lakes, this bacterial lineage is abundant from the surface waters (epilimnion) down to a 300-m depth (hypolimnion). UBA12189 appears to be free-living from CARD-FISH analysis. When compared to other genome-streamlined bacteria such as Nanopelagicales and Methylopumilus, genome reduction has caused UBA12189 to have a more limited metabolic repertoire in carbon, sulfur, and nitrogen metabolisms, limited numbers of membrane transporters, as well as a higher degree of auxotrophy for various amino acids, vitamins, and reduced sulfur. Despite having reduced genomes, UBA12189 encodes proteorhodopsin, complete biosynthesis pathways for heme and vitamin K2, cbb3-type cytochrome c oxidases, and heme-requiring enzymes. These genes may give a selective advantage during the genome streamlining process. We propose the new genus Acidiparvus, with two new species named "A. lacustris" and "A. fluvialis". Acidiparvus is the first described genome-streamlined lineage under the phylum Acidobacteriota, which is a free-living, slow-growing scavenger in freshwater environments.

Complete reference genome assemblies and annotations of three Escherichia coli MRE162 clones

Escherichia coli MRE162 was originally isolated from a toilet pan in 1949 and since been utilized in numerous studies. Here, we sequence, assemble, and annotate clones held at three laboratories providing reference-level assemblies. We show the uniqueness of MRE162 to strains in open databases and make the UK clone publically available.

Reference genome assembly and annotation of two Bacillus cereus sensu lato strains from Etosha National Park, Namibia

Bacillus cereus sensu lato (s.l.) poses health and security issues. Here, we report the reference genome assembly of two Bacillus cereus s.l. strains, isolated from Etosha National Park, Namibia (FFI_BCgr36 and FFI_BCgr46). These unique genomes open for better understanding of environmental diversity and improvements in detection of threatening species.

Nicotiana noctiflora Hook. Genome Contains Two Cellular T-DNAs with Functional Genes

Agrobacterium (Rhizobium)-mediated transformation leads to the formation of crown galls or hairy roots on infected plants. These effects develop due to the activity of T-DNA genes, gathered on a big plasmid, acquired from agrobacteria during horizontal gene transfer. However, a lot of plant species are known to contain such sequences, called cellular T-DNAs (cT-DNAs), and maintain normal phenotypes. Some of the genes remain intact, which leads to the conclusion of their functional role in plants. In this study, we present a comprehensive analysis of the cT-DNAs in the Nicotiana noctiflora Hook. genome, including gene expression and opine identification. Deep sequencing of the Nicotiana noctiflora genome revealed the presence of two different cT-DNAs, NnT-DNA1 and NnT-DNA2, which contain the intact genes iaaM, iaaH, acs, orf13, orf13a, and orf14. According to the expression analysis results, all these genes are most active in roots in comparison with other organs, which is consistent with data on cT-DNA gene expression in other plant species. We also used genetic engineering approaches and HPTLC and HPLC-MS methods to investigate the product of the acs gene (agrocinopine synthase), which turned out to be similar to agrocinopine A. Overall, this study expands our knowledge of cT-DNAs in plants and brings us closer to understanding their possible functions. Further research of cT-DNAs in different species and their functional implications could contribute to advancements in plant genetics and potentially unveil novel traits with practical applications in agriculture and other fields.

Chromosome-scale assemblies of S. malaccense, S. aqueum, S. jambos, and S. syzygioides provide insights into the evolution of Syzygium genomes

Syzygium is a large and diverse tree genus in the Myrtaceae family. Genome assemblies for clove (Syzygium aromaticum, 370 Mb) and sea apple (Syzygium grande, 405 Mb) provided the first insights into the genomic features and evolution of the Syzygium genus. Here, we present additional de novo chromosome-scale genome assemblies for Syzygium malaccense, Syzygium aqueum, Syzygium jambos, and Syzygium syzygioides. Genome profiling analyses show that S. malaccense, like S. aromaticum and S. grande, is diploid (2n = 2x = 22), while the S. aqueum, S. jambos, and S. syzygioides specimens are autotetraploid (2n = 4x = 44). The genome assemblies of S. malaccense (430 Mb), S. aqueum (392 Mb), S. jambos (426 Mb), and S. syzygioides (431 Mb) are highly complete (BUSCO scores of 98%). Comparative genomics analyses showed conserved organization of the 11 chromosomes with S. aromaticum and S. grande, and revealed species-specific evolutionary dynamics of the long terminal repeat retrotransposon elements belonging to the Gypsy and Copia lineages. This set of Syzygium genomes is a valuable resource for future structural and functional comparative genomic studies on Myrtaceae species.

Nuclear and Mitochondrial Genome Assemblies of the Beetle, Zygogramma bicolorata, a Globally Important Biocontrol Agent of Invasive Weed Parthenium hysterophorus

Implementing a genetic-based approach to achieve the full potential of classical biocontrol programs has been advocated for decades. The availability of genome-level information brings the opportunity to scrutinize biocontrol traits for their efficacy and evolvability. However, implementation of this advocacy remains limited to few instances. Biocontrol of a globally noxious weed, Parthenium hysterophorus, by the leaf-feeding beetle, Zygogramma bicolorata, has been in place for more than four decades now, with varying levels of success. As the first step in providing genetic-based improvement to this biocontrol program, we describe the nuclear and mitochondrial assemblies of Z. bicolorata. We assembled the genome from the long-read sequence data, error corrected with high-throughput short reads and checked for contaminants and sequence duplication to produce a 936 Mb nuclear genome. With 96.5% Benchmarking Universal Single-Copy Orthologs completeness and the long terminal repeat assembly index 12.91, we present a reference-quality assembly that appeared to be repeat rich at 62.7% genome-wide and consists of 29,437 protein-coding regions. We detected signature of nuclear insertion of mitochondrial fragments in 80 nuclear positions comprising 13 kb out of 17.9 kb mitochondria genome sequence. This genome, along with its annotations, provides a valuable resource to gain further insights into the biocontrol traits of Z. bicolorata for improving the control of the invasive weed P. hysterophorus.