Completing Circular Bacterial Genomes With Assembly Complexity by Using a Sampling Strategy From a Single MinION Run With Barcoding

Gut microbes with the gbu genes determine TMAO production from L-carnitine intake and serve as a biomarker for precision nutrition

Gut microbial metabolism of L-carnitine, which leads to the production of detrimental trimethylamine N-oxide (TMAO), offers a plausible link between red meat consumption and cardiovascular risks. Several microbial genes, including cntA/B, the cai operon, and the recently identified gbu gene cluster, have been implicated in the conversion of dietary L-carnitine into TMA(O). However, the key microbial genes and associated gut microbes involved in this pathway have not been fully explored. Utilizing the oral carnitine challenge test (OCCT), which specifically measures TMAO production from L-carnitine intake and identifies TMAO producer phenotypes, we compared the abundance of microbial genes between low- and high-TMAO producers across three independent cohorts. Our findings consistently revealed that the gbu gene cluster, rather than cntA/B or the cai operon, was significantly enriched in high-TMAO producers. We further analyzed 292 paired multi-omic datasets from OCCT and shotgun metagenomic sequencing, which demonstrated a significant positive correlation between the abundance of fecal gbu genes and L-carnitine-induced TMAO production, with gbuB showing the strongest correlation. Interestingly, these fecal gbu genes were found to increase with L-carnitine supplementation and decrease with a plant-based diet. Notably, we verified a previously uncultured gbu-containing bacterium, JAGTTR01 sp018223385, as the major contributor to TMA formation in the human gut. We isolated these gbu-containing gut microbes and confirmed their role in TMA/TMAO production using anaerobic incubation and a gnotobiotic mouse model. Using an in-house collection of gbu-containing isolates, we developed a qPCR-based method to quantify fecal gbuB and validated its correlation with L-carnitine-mediated TMAO production as measured by OCCT. Overall, these findings suggest that gbu-containing gut microbes are crucial for TMAO increases following L-carnitine intake and may serve as biomarkers or targets for personalized nutrition.

Detection in Orchards of Predominant Azole-Resistant Candida tropicalis Genotype Causing Human Candidemia, Taiwan

Fluconazole-resistant clade 4 Candida tropicalis causing candidemia in humans has been detected in tropical/subtropical areas, including those in China, Singapore, and Australia. We analyzed 704 individual yeasts isolated from fruits, soil, water, and farmers at 80 orchards in Taiwan. The most common pathogenic yeast species among 251 isolates recovered from farmers were Candida albicans (14.7%) and C. parapsilosis (11.6%). In contrast, C. tropicalis (13.0%), C. palmioleophila (6.6%), and Pichia kudriavzevii (6.0%) were prevalent among 453 environmental isolates. Approximately 18.6% (11/59) of C. tropicalis from the environment were resistant to fluconazole, and 81.8% (9/11) of those belonged to the clade 4 genotype. C. tropicalis susceptibility to fluconazole correlated with susceptibilities to the agricultural azole fungicides, difenoconazole, tebuconazole, and triadimenol. Tandem gene duplications of mutated ERG11 contributed to azole resistance. Agriculture environments are a reservoir for azole-resistant C. tropicalis; discontinuing agricultural use of azoles might reduce emergence of azole-resistant Candida spp. strains in humans.

DNA Sequencing Technologies and DNA Barcoding

DNA barcodes are short, standardized DNA segments that geneticists can use to identify all living taxa. On the other hand, DNA barcoding identifies species by analyzing these specific regions against a DNA barcode reference library. In its initial years, DNA barcodes sequenced by Sanger's method were extensively used by taxonomists for the characterization and identification of species. But in recent years, DNA barcoding by next-generation sequencing (NGS) has found broader applications, such as quality control, biomonitoring of protected species, and biodiversity assessment. Technological advancements have also paved the way to metabarcoding, which has enabled massive parallel sequ.encing of complex bulk samples using high-throughput sequencing techniques. In future, DNA barcoding along with high-throughput techniques will show stupendous progress in taxonomic classification with reference to available sequence data.

Isolation of Spirosoma foliorum sp. nov. from the fallen leaf of Acer palmatum by a novel cultivation technique

In the effort of isolating novel microbial species, the strain PL0132T was isolated from a fallen leaf under fresh water at a stream, which glided when grown on a tap water medium (without nutrients). The strain was determined to be Gram-negative, strictly aerobic, and rod-shaped, which grew optimally at 25 °C, pH 6-7, and the strain tolerates 1% (w/v) NaCl concentration. The complete genome of strain PL0132T comprises one contig with a sequencing depth of 76×, consisting of 8,853,064 base pairs and the genomic DNA G + C content was 46.7% (genome). 16S rRNA gene sequence analysis revealed that strain PL0132T represents a member of the phylum Bacteroidetes and is affiliated with the genus Spirosoma. Based on genomic, phenotypic, and chemotaxonomic characteristics, the strain PL0132T represents a novel species of the genus Spirosoma, for which the name Spirosoma foliorum sp. nov. is proposed (= KCTC 72228 T = InaCC B1447T).

Polymyxin resistance caused by large-scale genomic inversion due to IS26 intramolecular translocation in Klebsiella pneumoniae

Polymyxin B and polymyxin E (colistin) are presently considered the last line of defense against human infections caused by multidrug-resistant Gram-negative organisms such as carbapenemase-producer Enterobacterales, Acinetobacter baumannii, and Klebsiella pneumoniae. Yet resistance to this last-line drugs is a major public health threat and is rapidly increasing. Polymyxin S2 (S2) is a polymyxin B analogue previously synthesized in our institute with obviously high antibacterial activity and lower toxicity than polymyxin B and colistin. To predict the possible resistant mechanism of S2 for wide clinical application, we experimentally induced bacterial resistant mutants and studied the preliminary resistance mechanisms. Mut-S, a resistant mutant of K. pneumoniae ATCC BAA-2146 (Kpn2146) induced by S2, was analyzed by whole genome sequencing, transcriptomics, mass spectrometry and complementation experiment. Surprisingly, large-scale genomic inversion (LSGI) of approximately 1.1 Mbp in the chromosome caused by IS26 mediated intramolecular transposition was found in Mut-S, which led to mgrB truncation, lipid A modification and hence S2 resistance. The resistance can be complemented by plasmid carrying intact mgrB. The same mechanism was also found in polymyxin B and colistin induced drug-resistant mutants of Kpn2146 (Mut-B and Mut-E, respectively). This is the first report of polymyxin resistance caused by IS26 intramolecular transposition mediated mgrB truncation in chromosome in K. pneumoniae. The findings broaden our scope of knowledge for polymyxin resistance and enriched our understanding of how bacteria can manage to survive in the presence of antibiotics.

Portable nanopore-sequencing technology: Trends in development and applications

Sequencing technology is the most commonly used technology in molecular biology research and an essential pillar for the development and applications of molecular biology. Since 1977, when the first generation of sequencing technology opened the door to interpreting the genetic code, sequencing technology has been developing for three generations. It has applications in all aspects of life and scientific research, such as disease diagnosis, drug target discovery, pathological research, species protection, and SARS-CoV-2 detection. However, the first- and second-generation sequencing technology relied on fluorescence detection systems and DNA polymerization enzyme systems, which increased the cost of sequencing technology and limited its scope of applications. The third-generation sequencing technology performs PCR-free and single-molecule sequencing, but it still depends on the fluorescence detection device. To break through these limitations, researchers have made arduous efforts to develop a new advanced portable sequencing technology represented by nanopore sequencing. Nanopore technology has the advantages of small size and convenient portability, independent of biochemical reagents, and direct reading using physical methods. This paper reviews the research and development process of nanopore sequencing technology (NST) from the laboratory to commercially viable tools; discusses the main types of nanopore sequencing technologies and their various applications in solving a wide range of real-world problems. In addition, the paper collates the analysis tools necessary for performing different processing tasks in nanopore sequencing. Finally, we highlight the challenges of NST and its future research and application directions.

DNA barcoding, an effective tool for species identification: a review

DNA barcoding is a powerful taxonomic tool to identify and discover species. DNA barcoding utilizes one or more standardized short DNA regions for taxon identification. With the emergence of new sequencing techniques, such as Next-generation sequencing (NGS), ONT MinION nanopore sequencing, and Pac Bio sequencing, DNA barcoding has become more accurate, fast, and reliable. Rapid species identification by DNA barcodes has been used in a variety of fields, including forensic science, control of the food supply chain, and disease understanding. The Consortium for Barcode of Life (CBOL) presents various working groups to identify the universal barcode gene, such as COI in metazoans; rbcL, matK, and ITS in plants; ITS in fungi; 16S rRNA gene in bacteria and archaea, and creating a reference DNA barcode library. In this article, an attempt has been made to analyze the various proposed DNA barcode for different organisms, strengths & limitations, recent advancements in DNA barcoding, and methods to speed up the DNA barcode reference library construction. This study concludes that constructing a reference library with high species coverage would be a major step toward identifying species by DNA barcodes. This can be achieved in a short period of time by using advanced sequencing and data analysis methods.

Optimized conditions for Listeria, Salmonella and Escherichia whole genome sequencing using the Illumina iSeq100 platform with point-and-click bioinformatic analysis

Whole-genome sequencing (WGS) data have become an integral component of public health investigations and clinical diagnostics. Still, many veterinary diagnostic laboratories cannot afford to implement next generation sequencing (NGS) due to its high cost and the lack of bioinformatic knowledge of the personnel to analyze NGS data. Trying to overcome these problems, and make NGS accessible to every diagnostic laboratory, thirteen veterinary diagnostic laboratories across the United States (US) initiated the assessment of Illumina iSeq100 sequencing platform for whole genome sequencing of important zoonotic foodborne pathogens Escherichia coli, Listeria monocytogenes, and Salmonella enterica. The work presented in this manuscript is a continuation of this multi-laboratory effort. Here, seven AAVLD accredited diagnostic laboratories explored a further reduction in sequencing costs and the usage of user-friendly platforms for genomic data analysis. Our investigation showed that the same genomic library quality could be achieved by using a quarter of the recommended reagent volume and, therefore a fraction of the actual price, and confirmed that Illumina iSeq100 is the most affordable sequencing technology for laboratories with low WGS demand. Furthermore, we prepared step-by-step protocols for genomic data analysis in three popular user-friendly software (BaseSpace, Geneious, and GalaxyTrakr), and we compared the outcomes in terms of genome assembly quality, and species and antimicrobial resistance gene (AMR) identification. No significant differences were found in assembly quality, and the three analysis methods could identify the target bacteria species. However, antimicrobial resistance genes were only identified using BaseSpace and GalaxyTrakr; and GalaxyTrakr was the best tool for this task.

A comprehensive update to the Mycobacterium tuberculosis H37Rv reference genome

H37Rv is the most widely used Mycobacterium tuberculosis strain, and its genome is globally used as the M. tuberculosis reference sequence. Here, we present Bact-Builder, a pipeline that uses consensus building to generate complete and accurate bacterial genome sequences and apply it to three independently cultured and sequenced H37Rv aliquots of a single laboratory stock. Two of the 4,417,942 base-pair long H37Rv assemblies are 100% identical, with the third differing by a single nucleotide. Compared to the existing H37Rv reference, the new sequence contains ~6.4 kb additional base pairs, encoding ten new regions that include insertions in PE/PPE genes and new paralogs of esxN and esxJ, which are differentially expressed compared to the reference genes. New sequencing and de novo assemblies with Bact-Builder confirm that all 10 regions, plus small additional polymorphisms, are also present in the commonly used H37Rv strains NR123, TMC102, and H37Rv1998. Thus, Bact-Builder shows promise as an improved method to perform accurate and reproducible de novo assemblies of bacterial genomes, and our work provides important updates to the primary M. tuberculosis reference genome.

Distribution and Genomic Characterization of Third-Generation Cephalosporin-Resistant Escherichia coli Isolated from A Single Family and Home Environment: A 2-Year Longitudinal Study

Third-generation cephalosporin-resistant Escherichia coli (CREC), particularly strains producing extended-spectrum β-lactamases (ESBLs), are a global concern. Our study aims to longitudinally assemble the genomic characteristics of CREC isolates from fecal samples from an index patient with recurrent CREC-related urinary tract infections and his family and swabs from his home environment 12 times between 2019 and 2021 to investigate the distribution of antibiotic resistance genes. CREC identified using the VITEK 2 were subjected to nanopore whole-genome sequencing (WGS). The WGS of 27 CREC isolates discovered in 137 specimens (1 urine, 123 feces, and 13 environmental) revealed the predominance of ST101 and ST131. Among these sequence types, bla_CTX-M (44.4%, n = 12) was the predominant ESBL gene family, with bla_CTX-M-14 (n = 6) being the most common. The remaining 15 (55.6%) isolates harbored bla_CMY-2 genes and were clonally diverse. All E. coli isolated from the index patient’s initial urine and fecal samples belonged to O25b:H4-B2-ST131 and carried bla_CTX-M-14. The results of sequence analysis indicate plasmid-mediated household transmission of bla_CMY-2 or bla_CTX-M-55. A strong genomic similarity was discovered between fecal ESBL-producing E. coli and uropathogenic strains. Furthermore, bla_CMY-2 genes were widely distributed among the CREC isolated from family members and their home environment.

Nanopore Sequencing for De Novo Bacterial Genome Assembly and Search for Single-Nucleotide Polymorphism

Nanopore sequencing (ONT) is a new and rapidly developing method for determining nucleotide sequences in DNA and RNA. It serves the ability to obtain long reads of thousands of nucleotides without assembly and amplification during sequencing compared to next-generation sequencing. Nanopore sequencing can help for determination of genetic changes leading to antibiotics resistance. This study presents the application of ONT technology in the assembly of an E. coli genome characterized by a deletion of the tolC gene and known single-nucleotide variations leading to antibiotic resistance, in the absence of a reference genome. We performed benchmark studies to determine minimum coverage depth to obtain a complete genome, depending on the quality of the ONT data. A comparison of existing programs was carried out. It was shown that the Flye program demonstrates plausible assembly results relative to others (Shasta, Canu, and Necat). The required coverage depth for successful assembly strongly depends on the size of reads. When using high-quality samples with an average read length of 8 Kbp or more, the coverage depth of 30× is sufficient to assemble the complete genome de novo and reliably determine single-nucleotide variations in it. For samples with shorter reads with mean lengths of 2 Kbp, a higher coverage depth of 50× is required. Avoiding of mechanical mixing is obligatory for samples preparation. Nanopore sequencing can be used alone to determine antibiotics-resistant genetic features of bacterial strains.

Proof of concept for multiplex amplicon sequencing for mutation identification using the MinION nanopore sequencer

Rapid, cost-effective identification of genetic variants in small candidate genomic regions remains a challenge, particularly for less well equipped or lower throughput laboratories. The application of Oxford Nanopore Technologies’ MinION sequencer has the potential to fulfil this requirement. We demonstrate a proof of concept for a multiplexing assay that pools PCR amplicons for MinION sequencing to enable sequencing of multiple templates from multiple individuals, which could be applied to gene-targeted diagnostics. A combined strategy of barcoding and sample pooling was developed for simultaneous multiplex MinION sequencing of 100 PCR amplicons. The amplicons are family-specific, spanning a total of 30 loci in DNA isolated from 82 human neurodevelopmental cases and family members. The target regions were chosen for further interrogation because a potentially disease-causative variant had been identified in affected individuals following Illumina exome sequencing. The pooled MinION sequences were deconvoluted by aligning to custom references using the minimap2 aligner software. Our multiplexing approach produced an interpretable and expected sequence from 29 of the 30 targeted genetic loci. The sequence variant which was not correctly resolved in the MinION sequence was adjacent to a five nucleotide homopolymer. It is already known that homopolymers present a resolution problem with the MinION approach. Interestingly despite equimolar quantities of PCR amplicon pooled for sequencing, significant variation in the depth of coverage (127×–19,626×; mean = 8321×, std err = 452.99) was observed. We observed independent relationships between depth of coverage and target length, and depth of coverage and GC content. These relationships demonstrate biases of the MinION sequencer for longer templates and those with lower GC content. We demonstrate an efficient approach for variant discovery or confirmation from short DNA templates using the MinION sequencing device. With less than 130 × depth of coverage required for accurate genotyping, the methodology described here allows for rapid highly multiplexed targeted sequencing of large numbers of samples in a minimally equipped laboratory with a potential cost as much 200 × less than that from Sanger sequencing.

High molecular weight DNA extraction methods lead to high quality filamentous ascomycete fungal genome assemblies using Oxford Nanopore sequencing

During the last two decades, whole-genome sequencing has revolutionized genetic research in all kingdoms, including fungi. More than 1000 fungal genomes have been submitted to sequence databases, mostly obtained through second generation short-read DNA sequencing. As a result, highly fragmented genome drafts have typically been obtained. However, with the emergence of third generation long-read DNA sequencing, the assembly challenge can be overcome and highly contiguous assemblies obtained. Such attractive results, however, are extremely dependent on the ability to extract highly purified high molecular weight (HMW) DNA. Extraction of such DNA is currently a significant challenge for all species with cell walls, not least fungi. In this study, four isolates of filamentous ascomycetes (Apiospora pterospermum, Aspergillus sp. (subgen. Cremei), Aspergillus westerdijkiae, and Penicillium aurantiogriseum) were used to develop extraction and purification methods that result in HMW DNA suitable for third generation sequencing. We have tested and propose two straightforward extraction methods based on treatment with either a commercial kit or traditional phenol-chloroform extraction both in combination with a single commercial purification method that result in high quality HMW DNA from filamentous ascomycetes. Our results demonstrated that using these DNA extraction methods and coverage, above 75 x of our haploid filamentous ascomycete fungal genomes result in complete and contiguous assemblies.

Factors Affecting the Quality of Bacterial Genomes Assemblies by Canu after Nanopore Sequencing

Long-read sequencing (LRS), like Oxford Nanopore Technologies, is usually associated with higher error rates compared to previous generations. Factors affecting the assembly quality are the integrity of DNA, the flowcell efficiency, and, not least all, the raw data processing. Among LRS-intended de novo assemblers, Canu is highly flexible, with its dozens of adjustable parameters. Different Canu parameters were compared for assembling reads of Salmonellaenterica ser. Bovismorbificans (genome size of 4.8 Mbp) from three runs on MinION (N50 651, 805, and 5573). Two of them, with low quality and highly fragmented DNA, were not usable alone for assembly, while they were successfully assembled when combining the reads from all experiments. The best results were obtained by modifying Canu parameters related to the error correction, such as corErrorRate (exclusion of overlaps above a set error rate, set up at 0.40), corMhapSensitivity (the coarse sensitivity level, set to “high”), corMinCoverage (set to 0 to correct all reads, regardless the overlaps length), and corOutCoverage (corrects the longest reads up to the imposed coverage, set to 100). This setting produced two contigs corresponding to the complete sequences of the chromosome and a plasmid. The overall results highlight the importance of a tailored bioinformatic analysis.

MicroPIPE: validating an end-to-end workflow for high-quality complete bacterial genome construction

Background

Oxford Nanopore Technology (ONT) long-read sequencing has become a popular platform for microbial researchers due to the accessibility and affordability of its devices. However, easy and automated construction of high-quality bacterial genomes using nanopore reads remains challenging. Here we aimed to create a reproducible end-to-end bacterial genome assembly pipeline using ONT in combination with Illumina sequencing.

Results

We evaluated the performance of several popular tools used during genome reconstruction, including base-calling, filtering, assembly, and polishing. We also assessed overall genome accuracy using ONT both natively and with Illumina. All steps were validated using the high-quality complete reference genome for the Escherichia coli sequence type (ST)131 strain EC958. Software chosen at each stage were incorporated into our final pipeline, MicroPIPE.

Further validation of MicroPIPE was carried out using 11 additional ST131 E. coli isolates, which demonstrated that complete circularised chromosomes and plasmids could be achieved without manual intervention. Twelve publicly available Gram-negative and Gram-positive bacterial genomes (with available raw ONT data and matched complete genomes) were also assembled using MicroPIPE. We found that revised basecalling and updated assembly of the majority of these genomes resulted in improved accuracy compared to the current publicly available complete genomes.

Conclusions

MicroPIPE is built in modules using Singularity container images and the bioinformatics workflow manager Nextflow, allowing changes and adjustments to be made in response to future tool development. Overall, MicroPIPE provides an easy-access, end-to-end solution for attaining high-quality bacterial genomes. MicroPIPE is available at https://github.com/BeatsonLab-MicrobialGenomics/micropipe.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07767-z.

nanoMLST: accurate multilocus sequence typing using Oxford Nanopore Technologies MinION with a dual-barcode approach to multiplex large numbers of samples

Multilocus sequence typing (MLST) is one of the most commonly used methods for studying microbial lineage worldwide. However, the traditional MLST process using Sanger sequencing is time-consuming and expensive. We have designed a workflow that simultaneously sequenced seven full-length housekeeping genes of 96 meticillin-resistant Staphylococcus aureus isolates with dual-barcode multiplexing using just a single flow cell of an Oxford Nanopore Technologies MinION system, and then we performed bioinformatic analysis for strain typing. Fifty-one of the isolates comprising 34 sequence types had been characterized using Sanger sequencing. We demonstrate that the allele assignments obtained by our nanopore workflow (nanoMLST, available at https://github.com/jade-nhri/nanoMLST) were identical to those obtained by Sanger sequencing (359/359, with 100 % agreement rate). In addition, we estimate that our multiplex system is able to perform MLST for up to 1000 samples simultaneously; thus, providing a rapid and cost-effective solution for molecular typing.

A phased Vanilla planifolia genome enables genetic improvement of flavour and production

The global supply of vanilla extract is primarily sourced from the cured beans of the tropical orchid species Vanilla planifolia. Vanilla plants were collected from Mesoamerica, clonally propagated and globally distributed as part of the early spice trade. Today, the global food and beverage industry depends on descendants of these original plants that have not generally benefited from genetic improvement. As a result, vanilla growers and processors struggle to meet global demand for vanilla extract and are challenged by inefficient and unsustainable production practices. Here, we report a chromosome-scale, phased V. planifolia genome, which reveals sequence variants for genes that may impact the vanillin pathway and therefore influence bean quality. Resequencing of related vanilla species, including the minor commercial species Vanilla × tahitensis, identified genes that could impact productivity and post-harvest losses through pod dehiscence, flower anatomy and disease resistance. The vanilla genome reported in this study may enable accelerated breeding of vanilla to improve high-value traits.