Nanopore Sequencing Is a Credible Alternative to Recover Complete Genomes of Geminiviruses

Deciphering mixed infections by plant RNA virus and reconstructing complete genomes simultaneously present within-host

Local co-circulation of multiple phylogenetic lineages is particularly likely for rapidly evolving pathogens in the current context of globalisation. When different phylogenetic lineages co-occur in the same fields, they may be simultaneously present in the same host plant (i.e. mixed infection), with potentially important consequences for disease outcome. This is the case in Burkina Faso for the rice yellow mottle virus (RYMV), which is endemic to Africa and a major constraint on rice production. We aimed to decipher the distinct RYMV isolates that simultaneously infect a single rice plant and to sequence their genomes. To this end, we tested different sequencing strategies, and we finally combined direct cDNA ONT (Oxford Nanopore Technology) sequencing with the bioinformatics tool RVhaplo. This method was validated by the successful reconstruction of two viral genomes that were less than a hundred nucleotides apart (out of a genome of 4450nt length, i.e. 2-3%), and present in artificial mixes at a ratio of up to a 99/1. We then used this method to subsequently analyze mixed infections from field samples, revealing up to three RYMV isolates within one single rice plant sample from Burkina Faso. In most cases, the complete genome sequences were obtained, which is particularly important for a better estimation of viral diversity and the detection of recombination events. The method described thus allows to identify various haplotypes of RYMV simultaneously infecting a single rice plant, obtaining their full-length sequences, as well as a rough estimate of relative frequencies within the sample. It is efficient, cost-effective, as well as portable, so that it could further be implemented where RYMV is endemic. Prospects include unravelling mixed infections with other RNA viruses that threaten crop production worldwide.

Increase of niche filling with increase of host richness for plant-infecting mastreviruses

Now that it has been realized that viruses are ubiquitous, questions have been raised on factors influencing their diversity and distribution. For phytoviruses, understanding the interplay between plant diversity and virus species richness and prevalence remains cardinal. As both the amplification and the dilution of viral species richness due to increasing host diversity have been theorized and observed, a deeper understanding of how plants and viruses interact in natural environments is needed to explore how host availability conditions viral diversity and distributions. From a unique dataset, this study explores interactions of Mastrevirus species (family Geminiviridae) with Poales order hosts across 10 sites from three contrasting ecosystems on La Réunion. Among 273 plant pools, representing 61 Poales species, 15 Mastrevirus species were characterized from 22 hosts. The analysis revealed a strong association of mastreviruses with hosts from agroecosystems, the rare presence of viruses in coastal grasslands, and the absence of mastreviruses in subalpine areas, areas dominated by native plants. This suggests that detected mastreviruses were introduced through anthropogenic activities, emphasizing the role of humans in shaping the global pathobiome. By reconstructing the realized host-virus infection network, besides revealing a pattern of increasing viral richness with increasing host richness, we observed increasing viral niche occupancies with increasing host species richness, implying that virus realized richness at any given site is conditioned on the global capacity of the plant populations to host diverse mastreviruses. Whether this tendency is driven by synergy between viruses or by an interplay between vector population and plant richness remains to be established.

An Alarming Eastward Front of Cassava Mosaic Disease in Development in West Africa

Begomoviruses are a major threat to cassava production in Africa. Indeed, during the 1990s, the emergence of a recombinant begomovirus (East African cassava mosaic virus-Uganda, EACMV-Ug) resulted in crop devastation and severe famine in Uganda. In 2023, during a pre-survey of cassava farms at Forécariah, South-West Guinea, 22 samples showing peculiar cassava mosaic disease (CMD) symptoms were collected, and subsequent laboratory analysis confirmed the presence of EACMV-Ug in the samples. Deep analysis of DNA-A and DNA-B of the EACMV-Ug isolates from Guinea indicated that they are similar to those associated with the severe CMD epidemic in Uganda in the 1990s. Therefore, a country-wide survey was conducted throughout Guinea in April 2024 to evaluate the extent of the spread of EACMV-Ug in the country and to collect critical CMD epidemiological data. Findings showed a high whitefly population in Lower Guinea averaging 17 per plant; however, the data suggest a spread of EACMV-Ug via infected cuttings. High CMD incidence was found in Lower Guinea and Forest Guinea, whereas the highest CMD severity was observed in Forest Guinea (2.70 ± 0.06) and the lowest CMD severity was found in Middle Guinea (2.20 ± 0.05). Several cases of double and triple infections involving African cassava mosaic virus, East African cassava mosaic virus, East African cassava mosaic Cameroon virus, and EACMV-Ug were observed. EACMV-Ug was detected throughout Guinea, as well as from samples collected in 2022 in Kambia (Sierra Leone). The 63 accessions cultivated in Guinea that were assessed in this study were found susceptible to at least one of the viruses cited above. This study alerts us to an alarming situation in development in West Africa and provides scientific evidence to guide the rapid response needed to contain and stop the progression of EACMV-Ug in West Africa.

Distributions, interactions, and dynamics of prokaryotes and phages in a hybrid biological wastewater treatment system

BACKGROUND

Understanding the interactions and dynamics of microbiotas within biological wastewater treatment systems is essential for ensuring their stability and long-term sustainability. In this study, we developed a systematic framework employing multi-omics and Hi-C sequencing to extensively investigate prokaryotic and phage communities within a hybrid biofilm and activated sludge system.

RESULTS

We uncovered distinct distribution patterns, metabolic capabilities, and activities of functional prokaryotes through the analysis of 454 reconstructed prokaryotic genomes. Additionally, we reconstructed a phage catalog comprising 18,645 viral operational taxonomic units (vOTUs) with high length and contiguity using hybrid assembly, and a distinct distribution of phages was depicted between activated sludge (AS) and biofilm. Importantly, 1340 host-phage pairs were established using Hi-C and conventional in silico methods, unveiling the host-determined phage prevalence. The majority of predicted hosts were found to be involved in various crucial metabolic processes, highlighting the potential vital roles of phages in influencing substance metabolism within this system. Moreover, auxiliary metabolic genes (AMGs) related to various categories (e.g., carbohydrate degradation, sulfur metabolism, transporter) were predicted. Subsequent activity analysis emphasized their potential ability to mediate host metabolism during infection. We also profiled the temporal dynamics of phages and their associated hosts using 13-month time-series metagenomic data, further demonstrating their tight interactions. Notably, we observed lineage-specific infection patterns, such as potentially host abundance- or phage/host ratio-driven phage population changes.

CONCLUSIONS

The insights gained from this research contribute to the growing body of knowledge surrounding interactions and dynamics of host-phage and pave the way for further exploration and potential applications in the field of microbial ecology. Video Abstract.

Identification of Viruses Infecting Phalaenopsis Orchids Using Nanopore Sequencing and Development of an RT-RPA-CRISPR/Cas12a for Rapid Visual Detection of Nerine Latent Virus

Phalaenopsis orchids are one of the most popular ornamental plants. More than thirty orchid viruses have been reported, and virus-infected Phalaenopsis orchids significantly lose their commercial value. Therefore, the development of improved viral disease detection methods could be useful for quality control in orchid cultivation. In this study, we first utilized the MinION, a portable sequencing device based on Oxford Nanopore Technologies (ONT) to rapidly detect plant viruses in Phalaenopsis orchids. Nanopore sequencing revealed the presence of three plant viruses in Phalaenopsis orchids: odontoglossum ringspot virus, cymbidium mosaic virus, and nerine latent virus (NeLV). Furthermore, for the first time, we detected NeLV infection in Phalaenopsis orchids using nanopore sequencing and developed the reverse transcription-recombinase polymerase amplification (RT-RPA)-CRISPR/Cas12a method for rapid, instrument-flexible, and accurate diagnosis. The developed RT-RPA-CRISPR/Cas12a technique can confirm NeLV infection in less than 20 min and exhibits no cross-reactivity with other viruses. To determine the sensitivity of RT-RPA-CRISPR/Cas12a for NeLV, we compared it with RT-PCR using serially diluted transcripts and found a detection limit of 10 zg/μL, which is approximately 1000-fold more sensitive. Taken together, the ONT platform offers an efficient strategy for monitoring plant viral pathogens, and the RT-RPA-CRISPR/Cas12a method has great potential as a useful tool for the rapid and sensitive diagnosis of NeLV.

Hybrid RNA sequencing of broad bean wilt virus 2 from faba beans

IMPORTANCE

Globally, viral diseases impair the growth and vigor of cultivated crops such as grains, leading to a significant reduction in quality, marketability, and competitiveness. As an island nation, Australia has a distinct advantage in using its border to prevent the introduction of damaging viruses, which threaten the continental agricultural sector. However, breeding programs in Australia rely on imported seeds as new sources of genetic diversity. As such, it is critical to remain vigilant in identifying new and emerging viral pathogens, by ensuring the availability of accurate genomic diagnostic tools at the grain biosecurity border. High-throughput sequencing offers game-changing opportunities in biosecurity routine testing. Genomic results are more accurate and informative compared to traditional molecular methods or biological indexing. The present work contributes to strengthening accurate phytosanitary screening, to safeguard the Australian grains industry, and expedite germplasm release to the end users.

NanoViromics: long-read sequencing of dsRNA for plant virus and viroid rapid detection

There is a global need for identifying viral pathogens, as well as for providing certified clean plant materials, in order to limit the spread of viral diseases. A key component of management programs for viral-like diseases is having a diagnostic tool that is quick, reliable, inexpensive, and easy to use. We have developed and validated a dsRNA-based nanopore sequencing protocol as a reliable method for detecting viruses and viroids in grapevines. We compared our method, which we term direct-cDNA sequencing from dsRNA (dsRNAcD), to direct RNA sequencing from rRNA-depleted total RNA (rdTotalRNA), and found that it provided more viral reads from infected samples. Indeed, dsRNAcD was able to detect all of the viruses and viroids detected using Illumina MiSeq sequencing (dsRNA-MiSeq). Furthermore, dsRNAcD sequencing was also able to detect low-abundance viruses that rdTotalRNA sequencing failed to detect. Additionally, rdTotalRNA sequencing resulted in a false-positive viroid identification due to the misannotation of a host-driven read. Two taxonomic classification workflows, DIAMOND & MEGAN (DIA & MEG) and Centrifuge & Recentrifuge (Cent & Rec), were also evaluated for quick and accurate read classification. Although the results from both workflows were similar, we identified pros and cons for both workflows. Our study shows that dsRNAcD sequencing and the proposed data analysis workflows are suitable for consistent detection of viruses and viroids, particularly in grapevines where mixed viral infections are common.

Evaluation of sequencing and PCR-based methods for the quantification of the viral genome formula

Viruses show great diversity in their genome organization. Multipartite viruses package their genome segments into separate particles, most or all of which are required to initiate infection in the host cell. The benefits of such seemingly inefficient genome organization are not well understood. One hypothesised benefit of multipartition is that it allows for flexible changes in gene expression by altering the frequency of each genome segment in different environments, such as encountering different host species. The ratio of the frequency of segments is termed the genome formula (GF). Thus far, formal studies quantifying the GF have been performed for well-characterised virus-host systems in experimental settings using RT-qPCR. However, to understand GF variation in natural populations or novel virus-host systems, a comparison of several methods for GF estimation including high-throughput sequencing (HTS) based methods is needed. Currently, it is unclear how HTS-methods compare a golden standard, such as RT-qPCR. Here we show a comparison of multiple GF quantification methods (RT-qPCR, RT-digital PCR, Illumina RNAseq and Nanopore direct RNA sequencing) using three host plants (Nicotiana tabacum, Nicotiana benthamiana, and Chenopodium quinoa) infected with cucumber mosaic virus (CMV), a tripartite RNA virus. Our results show that all methods give roughly similar results, though there is a significant method effect on genome formula estimates. While the RT-qPCR and RT-dPCR GF estimates are congruent, the GF estimates from HTS methods deviate from those found with PCR. Our findings emphasize the need to tailor the GF quantification method to the experimental aim, and highlight that it may not be possible to compare HTS and PCR-based methods directly. The difference in results between PCR-based methods and HTS highlights that the choice of quantification technique is not trivial.

Evaluation of tangential flow filtration coupled to long-read sequencing for ostreid herpesvirus type 1 genome assembly

Whole-genome sequencing is widely used to better understand the transmission dynamics, the evolution and the emergence of new variants of viral pathogens. This can bring crucial information to stakeholders for disease management. Unfortunately, aquatic virus genomes are usually difficult to characterize because most of these viruses cannot be easily propagated in vitro. Developing methodologies for routine genome sequencing of aquatic viruses is timely given the ongoing threat of disease emergence. This is particularly true for pathogenic viruses infecting species of commercial interest that are widely exchanged between production basins or countries. For example, the ostreid herpesvirus type 1 (OsHV-1) is a Herpesvirus widely associated with mass mortality events of juvenile Pacific oyster Crassostrea gigas. Genomes of Herpesviruses are large and complex with long direct and inverted terminal repeats. In addition, OsHV-1 is unculturable. It therefore accumulates several features that make its genome sequencing and assembly challenging. To overcome these difficulties, we developed a tangential flow filtration (TFF) method to enrich OsHV-1 infective particles from infected host tissues. This virus purification allowed us to extract high molecular weight and high-quality viral DNA that was subjected to Illumina short-read and Nanopore long-read sequencing. Dedicated bioinformatic pipelines were developed to assemble complete OsHV-1 genomes with reads from both sequencing technologies. Nanopore sequencing allowed characterization of new structural variations and major viral isomers while having 99,98 % of nucleotide identity with the Illumina assembled genome. Our study shows that TFF-based purification method, coupled with Nanopore sequencing, is a promising approach to enable in field sequencing of unculturable aquatic DNA virus.

Nanopore Metagenomics Sequencing for Rapid Diagnosis and Characterization of Lily Viruses

Lilies (Lilium spp.) are one of the most important ornamental flower crops grown in Korea. Most viral diseases in lilies are transmitted by infected bulbs, which cause serious economic losses due to reduced yields. Various diagnostic techniques and high-throughput sequencing methods have been used to detect lily viruses. According to Oxford Nanopore Technologies (ONT), MinION is a compact and portable sequencing device. In this study, three plant viruses, lily mottle, lily symptomless, and plantago asiatica mosaic virus, were detected in lily samples using the ONT platform. As a result of genome assembly of reads obtained through ONT, 100% coverage and 90.3-93.4% identity were obtained. Thus, we show that the ONT platform is a promising tool for the diagnosis and characterization of viruses that infect crops.

A balanced gut microbiota is essential to maintain health in captive sika deer

Certain animals harbor a high proportion of pathogens, particular the zoonotic pathogens, in their gut microbiome but are usually asymptomic; however, their carried pathogens may seriously threaten the public health. By understanding how the microbiome overcomes the negative effects of pathogens to maintain host health, we can develop novel solutions to control animal-mediated pathogen transmission including identification and application of beneficial microbes. Here, we analyzed the gut microbiota of 10 asymptomic captive sika deer individuals by full-length 16S rDNA sequencing. Twenty-nine known pathogens capable of infecting humans were identified, and the accumulated proportions of the identified pathogens were highly variable among individuals (2.33 to 39.94%). The relative abundances of several beneficial bacteria, including Lactobacillus and Bifidobacterium, were found to be positively correlated with the relative abundances of accumulated pathogens. Whole-genome metagenomic analysis revealed that the beneficial- and pathogenic-associated functions, such as genes involved in the synthesis of short chain fatty acids and virulence factors, were also positively correlated in the microbiome, indicating that the beneficial and pathogenic functions were maintained at a relatively balanced ratio. Furthermore, the bacteriophages that target the identified pathogens were found to be positively correlated with the pathogenic content in the microbiome. Several high-quality genomes of beneficial bacteria affiliated with Lactobacillus and Bifidobacterium and bacteriophages were recovered from the metagenomic data. Overall, this study provides novel insights into the interplay between beneficial and pathogenic content to ensure maintenance of a healthy gut microbiome, and also contributes to discovery of novel beneficial microbes and functions that control pathogens. KEY POINTS: • Certain asymptomic captive sika deer individuals harbor relatively high amounts of zoonotic pathogens. • The beneficial microbes and the beneficial functions are balanced with the pathogenic contents in the gut microbiome. • Several high-quality genomes of beneficial bacteria and bacteriophages are recovered by metagenomics.

Nanopore sequencing technology and its application in plant virus diagnostics

Plant viruses threaten crop yield and quality; thus, efficient and accurate pathogen diagnostics are critical for crop disease management and control. Recent advances in sequencing technology have revolutionized plant virus research. Metagenomics sequencing technology, represented by next-generation sequencing (NGS), has greatly enhanced the development of virus diagnostics research because of its high sensitivity, high throughput and non-sequence dependence. However, NGS-based virus identification protocols are limited by their high cost, labor intensiveness, and bulky equipment. In recent years, Oxford Nanopore Technologies and advances in third-generation sequencing technology have enabled direct, real-time sequencing of long DNA or RNA reads. Oxford Nanopore Technologies exhibit versatility in plant virus detection through their portable sequencers and flexible data analyses, thus are wildly used in plant virus surveillance, identification of new viruses, viral genome assembly, and evolution research. In this review, we discuss the applications of nanopore sequencing in plant virus diagnostics, as well as their limitations.

Rapid and Routine Molecular Typing Using Multiplex Polymerase Chain Reaction and MinION Sequencer

Molecular typing is an essential tool that has been extensively applied in laboratories as well as in clinical settings. Next-generation sequencing technologies promise high-throughput and cost-effective molecular applications; however, the accessibility of these technologies is limited due to the high capital cost. Oxford Nanopore Technologies (ONT) offers a MinION device with the advantages of real-time data analysis, rapid library preparation, and low cost per test. However, the advantages of the MinION device are often overshadowed by its lower raw accuracy. Herein, we present a concise multilocus sequence typing protocol of Staphylococcus aureus using multiplex polymerase chain reaction and Rapid Barcoding Kit for barcoding and MinION device for sequencing. Moreover, to clarify the effects of carryover DNA on tasks that require high sequence accuracy, we used the MinION flow cell in successive runs of washing and reusing. Our results revealed that the MinION flow cell could achieve accurate typing of a total of 467 samples with 3,269 kilobase-long genes within a total of 5 runs. This thus demonstrates the effectiveness of a portable nanopore MinION sequencer in providing accurate, rapid, and routine molecular typing.

CODEHOP-Mediated PCR Improves HIV-1 Genotyping and Detection of Variants by MinION Sequencing

HIV-1 is genetically heterogeneous, having different subtypes and circulating recombinant forms (CRFs). HIV-1 genotyping is used to determine drug resistance profiles and is based on the use of a mixture of consensus and degenerate primers targeting the pol gene. However, the use of this type of primers is associated with either PCR bias or PCR failure. Consensus-degenerate hybrid oligonucleotide primers (CODEHOPs) can detect and identify unknown and distantly related gene sequences by PCR. CODEHOPs designed using different HIV-1 subtypes and CRFs were evaluated for HIV-1 genotyping by Sanger and MinION sequencing. A total of 321 plasma samples were used for the validation of CODEHOP-mediated HIV-1 genotyping. CODEHOP-mediated PCR showed 100% sensitivity and specificity, with limits of detection and genotyping below 200 copies/ml. The head-to-head evaluation of CODEHOP-mediated PCR and standard PCR showed 97 to 98% and 82 to 84% PCR success rates, respectively. There was 100% agreement between the CODEHOP and the reference method in the drug resistance profiles determined by Sanger-based sequencing. Using MinION sequencing, the CODEHOP-mediated PCR scheme resulted in better depth of genome coverage and detection of more drug resistance variants in the protease and reverse transcriptase genes than the standard amplification scheme. The overall prevalences of drug resistance mutations were 17.1% in treatment-experienced patients and 1.2% in treatment-naive patients. They were mainly associated with resistance to reverse transcriptase inhibitors and were linked to virological failure and the patient’s treatment history. Findings from this study suggest that the performance of HIV-1 genotyping is improved by using CODEHOP-mediated PCR.

IMPORTANCE HIV-1 drug resistance is the main cause of treatment failure. Regular surveillance of resistance-associated mutations in HIV-1 genomes is essential for the optimal management of HIV-1 infections. Due to HIV-1’s genetic diversity, different HIV-1 genotypes are circulating worldwide. Standard primers used in the amplification of HIV-1 RNA have not been designed to cover all HIV-1 genotypes and are the main cause of amplification and drug resistance test failure. In this study, new sets of PCR primers targeting the protease, reverse transcriptase, and integrase genes were designed using the CODEHOP approach. They were compared to primers recommended in part by WHO for drug resistance testing using in-house PCR. Unsuccessful HIV-1 RNA amplification was less likely to occur with CODEHOP primers, leading to fewer test failures and lower cost. Furthermore, CODEHOP primers were more effective than standard primers for the detection of minority resistant variants by MinION sequencing.

Complete Genome Sequencing of Field Isolates of Peste des Petits Ruminants Virus from Tanzania Revealed a High Nucleotide Identity with Lineage III PPR Viruses

Peste des petits ruminants virus (PPRV) causes a highly devastating disease of sheep and goats that threatens food security, small ruminant production and susceptible endangered wild ruminants. With policy directed towards achieving global PPR eradication, the establishment of cost-effective genomic surveillance tools is critical where PPR is endemic. Genomic data can provide sufficient in-depth information to identify the pockets of endemicity responsible for PPRV persistence and viral evolution, and direct an appropriate vaccination response. Yet, access to the required sequencing technology is low in resource-limited settings and is compounded by the difficulty of transporting clinical samples from wildlife across international borders due to the Convention on International Trade in Endangered Species (CITES) of Wild Fauna and Flora, and Nagoya Protocol regulations. Oxford nanopore MinION sequencing technology has recently demonstrated an extraordinary performance in the sequencing of PPRV due to its rapidity, utility in endemic countries and comparatively low cost per sample when compared to other whole-genome (WGS) sequencing platforms. In the present study, Oxford nanopore MinION sequencing was utilised to generate complete genomes of PPRV isolates collected from infected goats in Ngorongoro and Momba districts in the northern and southern highlands of Tanzania during 2016 and 2018, respectively. The tiling multiplex polymerase chain reaction (PCR) was carried out with twenty-five pairs of long-read primers. The resulting PCR amplicons were used for nanopore library preparation and sequencing. The analysis of output data was complete genomes of PPRV, produced within four hours of sequencing (accession numbers: MW960272 and MZ322753). Phylogenetic analysis of the complete genomes revealed a high nucleotide identity, between 96.19 and 99.24% with lineage III PPRV currently circulating in East Africa, indicating a common origin. The Oxford nanopore MinION sequencer can be deployed to overcome diagnostic and surveillance challenges in the PPR Global Control and Eradication program. However, the coverage depth was uneven across the genome and amplicon dropout was observed mainly in the GC-rich region between the matrix (M) and fusion (F) genes of PPRV. Thus, larger field studies are needed to allow the collection of sufficient data to assess the robustness of nanopore sequencing technology.

Identification of full-length circular nucleic acids using long-read sequencing technologies

Unlike the traditional perception in genomic DNA or linear RNA, circular nucleic acids are a class of functional biomolecules with a circular configuration and are often observed in nature. These circular molecules encompass the full spectrum of size and play an important role in organisms, making circular nucleic acids research worthy. Due to the low abundance of most types of circular nucleic acids and the disadvantages of short-read sequencing platforms, accurate and full-length circular nucleic acid sequencing and identification is difficult. In this review, we have provided insights into full-length circular nucleic acid detection methods using long-read sequencing technologies, with a focus on the experimental and bioinformatics strategies to obtain accurate sequences.

Metagenomic Studies of Viruses in Weeds and Wild Plants: A Powerful Approach to Characterise Variable Virus Communities

High throughput sequencing (HTS) has revolutionised virus detection and discovery, allowing for the untargeted characterisation of whole viromes. Viral metagenomics studies have demonstrated the ubiquity of virus infection - often in the absence of disease symptoms - and tend to discover many novel viruses, highlighting the small fraction of virus biodiversity described to date. The majority of the studies using high-throughput sequencing to characterise plant viromes have focused on economically important crops, and only a small number of studies have considered weeds and wild plants. Characterising the viromes of wild plants is highly relevant, as these plants can affect disease dynamics in crops, often by acting as viral reservoirs. Moreover, the viruses in unmanaged systems may also have important effects on wild plant populations and communities. Here, we review metagenomic studies on weeds and wild plants to show the benefits and limitations of this approach and identify knowledge gaps. We consider key genomics developments that are likely to benefit the field in the near future. Although only a small number of HTS studies have been performed on weeds and wild plants, these studies have already discovered many novel viruses, demonstrated unexpected trends in virus distributions, and highlighted the potential of metagenomics as an approach.