June 1, 2021  |  

Accurately surveying uncultured microbial species with SMRT Sequencing

Background: Microbial ecology is reshaping our understanding of the natural world by revealing the large phylogenetic and functional diversity of microbial life. However the vast majority of these microorganisms remain poorly understood, as most cultivated representatives belong to just four phylogenetic groups and more than half of all identified phyla remain uncultivated. Characterization of this microbial ‘dark matter’ will thus greatly benefit from new metagenomic methods for in situ analysis. For example, sensitive high throughput methods for the characterization of community composition and structure from the sequencing of conserved marker genes. Methods: Here we utilize Single Molecule Real-Time (SMRT) sequencing of full-length 16S rRNA amplicons to phylogenetically profile microbial communities to below the genus-level. We test this method on a mock community of known composition, as well as a previously studied microbial community from a lake known to predominantly contain poorly characterized phyla. These results are compared to traditional 16S tag sequencing from short-read technologies and subsets of the full-length data corresponding to the same regions of the 16S gene. Results: We explore the benefits of using full-length amplicons for estimating community structure and diversity. In addition, we investigate the possible effects of context-specific and GC-content biases known to affect short-read sequencing technologies on the predicted community structure. We characterize the potential benefits of profiling metagenomic communities with full-length 16S rRNA genes from SMRT sequencing relative to standard methods.


June 1, 2021  |  

Reconstruction of the spinach coding genome using full-length transcriptome without a reference genome

For highly complex and large genomes, a well-annotated genome may be computationally challenging and costly, yet the study of alternative splicing events and gene annotations usually rely on the existence of a genome. Long-read sequencing technology provides new opportunities to sequence full-length cDNAs, avoiding computational challenges that short read transcript assembly brings. The use of single molecule, real-time sequencing from PacBio to sequence transcriptomes (the Iso-Seq method), which produces de novo, high-quality, full-length transcripts, has revealed an astonishing amount of alternative splicing in eukaryotic species. With the Iso-Seq method, it is now possible to reconstruct the transcribed regions of the genome using just the transcripts themselves. We present Cogent, a tool for finding gene families and reconstructing the coding genome in the absence of a high-quality reference genome. Cogent uses k-mer similarities to first partition the transcripts into different gene families. Then, for each gene family, the transcripts are used to build a splice graph. Cogent identifies bubbles resulting from sequencing errors, minor variants, and exon skipping events, and attempts to resolve each splice graph down to the minimal set of reconstructed contigs. We apply Cogent to the Iso-Seq data for spinach, Spinacia oleracea, for which there is also a PacBio-based draft genome to validate the reconstruction. The Iso-Seq dataset consists of 68,263 fulllength, Quiver-polished transcript sequences ranging from 528 bp to 6 kbp long (mean: 2.1 kbp). Using the genome mapping as ground truth, we found that 95% (8045/8446) of the Cogent gene families found corresponded to a single genomic loci. For families that contained multiple loci, they were often homologous genes that would be categorized as belonging to the same gene family. Coding genome reconstruction was then performed individually for each gene family. A total of 86% (7283/8446) of the gene families were resolved to a single contig by Cogent, and was validated to be also a single contig in the genome. In 59 cases, Cogent reconstructed a single contig, however the contig corresponded to 2 or more loci in the genome, suggesting possible scaffolding opportunities. In 24 cases, the transcripts had no hits to the genome, though Pfam and BLAST searches of the transcripts show that they were indeed coding, suggesting that the genome is missing certain coding portions. Given the high quality of the spinach genome, we were not surprised to find that Cogent only minorly improved the genome space. However the ability of Cogent to accurately identify gene families and reconstruct the coding genome in a de novo fashion shows that it will be extremely powerful when applied to datasets for which there is no or low-quality reference genome.


June 1, 2021  |  

Multiplexing strategies for microbial whole genome SMRT Sequencing

The increased throughput of the RS II and Sequel Systems enables multiple microbes to be sequenced on a single SMRT Cell. This multiplexing can be readily achieved by simply incorporating a unique barcode for each microbe into the SMRTbell adapters after shearing genomic DNA using a streamlined library construction process. Incorporating a barcode without the requirement for PCR amplification prevents the loss of epigenetic information (e.g., methylation signatures), and the generation of chimeric sequences, while the modified protocol eliminates the need to build several individual SMRTbell libraries. We multiplexed up to 8 unique strains of H. pylori. Each strain was sheared, and processed through adapter ligation in a single, addition only reaction. The barcoded strains were then pooled in equimolar quantities, and processed through the remainder of the library preparation and purification steps. We demonstrate successful de novo microbial assembly and epigenetic analysis from all multiplexes (2 through 8-plex) using standard tools within SMRT Link Analysis using data generated from a single SMRTbell library, run on a single SMRT Cell. This process facilitates the sequencing of multiple microbial genomes in a single day, greatly increasing throughput and reducing costs per genome assembly.


June 1, 2021  |  

Applying Sequel to Genomic Datasets

De novo assembly is a large part of JGI’s analysis portfolio. Repetitive DNA sequences are abundant in a wide range of organisms we sequence and pose a significant technical challenge for assembly. We are interested in long read technologies capable of spanning genomic repeats to produce better assemblies. We currently have three RS II and two Sequel PacBio machines. RS II machines are primarily used for fungal and microbial genome assembly as well as synthetic biology validation. Between microbes and fungi we produce hundreds of PacBio libraries a year and for throughput reasons the vast majority of these are >10 kb AMPure libraries. Throughput for RS II is about 1 Gb per SMRT Cell. This is ideal for microbial sized genomes but can be costly and labor intensive for larger projects which require multiple cells. JGI was an early access site for Sequel and began testing with real samples in January 2016. During that time we’ve had the opportunity to sequence microbes, fungi, metagenomes, and plants. Here we present our experience over the last 18 months using the Sequel platform and provide comparisons with RS II results.


June 1, 2021  |  

Comparative metagenome-assembled genome analysis of “Candidatus Lachnocurva vaginae”, formerly known as Bacterial Vaginosis Associated bacterium – 1 (BVAB1)

Bacterial Vaginosis Associated bacterium 1 (BVAB1) is an as-yet uncultured bacterial species found in the human vagina that belongs to the family Lachnospiraceae within the order Clostridiales. As its name suggests, this bacterium is often associated with bacterial vaginosis (BV), a common vaginal disorder that has been shown to increase a woman’s risk for HIV, Chlamydia trachomatis, and Neisseria gonorrhoeae infections as well as preterm birth. Further, BVAB1 is associated with the persistence of BV following metronidazole treatment, increased vaginal inflammation, and adverse obstetrics outcomes. There is no available complete genome sequence of BVAB1, which has made it di?cult to mechanistically understand its role in disease. We present here a circularized metagenome-assembled genome (cMAG) of B VAB1 as well as a comparative analysis including an additional six metagenome-assembled genomes (MAGs) of this species. These sequences were derived from cervicovaginal samples of seven separate women. The cMAG is 1.649 Mb in size and encodes 1,578 genes. We propose to rename BVAB1 to “Candidatus Lachnocurva vaginae” based on phylogenetic analyses, and provide genomic evidence that this candidate species may metabolize D-lactate, produce trimethylamine (one of the chemicals responsible for BV-associated odor), and be motile. The cMAG and the six MAGs are valuable resources that will further contribute to our understanding of the heterogeneous etiology of bacterial vaginosis.


April 21, 2020  |  

Chlorella vulgaris genome assembly and annotation reveals the molecular basis for metabolic acclimation to high light conditions.

Chlorella vulgaris is a fast-growing fresh-water microalga cultivated at the industrial scale for applications ranging from food to biofuel production. To advance our understanding of its biology and to establish genetics tools for biotechnological manipulation, we sequenced the nuclear and organelle genomes of Chlorella vulgaris 211/11P by combining next generation sequencing and optical mapping of isolated DNA molecules. This hybrid approach allowed to assemble the nuclear genome in 14 pseudo-molecules with an N50 of 2.8 Mb and 98.9% of scaffolded genome. The integration of RNA-seq data obtained at two different irradiances of growth (high light-HL versus low light -LL) enabled to identify 10,724 nuclear genes, coding for 11,082 transcripts. Moreover 121 and 48 genes were respectively found in the chloroplast and mitochondrial genome. Functional annotation and expression analysis of nuclear, chloroplast and mitochondrial genome sequences revealed peculiar features of Chlorella vulgaris. Evidence of horizontal gene transfers from chloroplast to mitochondrial genome was observed. Furthermore, comparative transcriptomic analyses of LL vs HL provide insights into the molecular basis for metabolic rearrangement in HL vs. LL conditions leading to enhanced de novo fatty acid biosynthesis and triacylglycerol accumulation. The occurrence of a cytosolic fatty acid biosynthetic pathway can be predicted and its upregulation upon HL exposure is observed, consistent with increased lipid amount under HL. These data provide a rich genetic resource for future genome editing studies, and potential targets for biotechnological manipulation of Chlorella vulgaris or other microalgae species to improve biomass and lipid productivity.This article is protected by copyright. All rights reserved.


April 21, 2020  |  

Complete genome sequence of Marinobacter sp. LQ44, a haloalkaliphilic phenol-degrading bacterium isolated from a deep-sea hydrothermal vent

Marinobacter sp. strain LQ44, an alkaliphile and moderate halophile from a deep-sea hydrothermal vent on the East Pacific Rise, is a novel phenol-degrading bacterium that is capable of utilizing phenol as sole carbon and energy sources. Here, we present the complete genome sequence of strain LQ44, which consists of 4,435,564?bp with a circular chromosome, 4164 protein-coding genes, 3 rRNA operons and 50 tRNAs. Genome analysis revealed that strain LQ44 may degrade phenol via meta-cleavage pathway. The LQ44 genome contains multiple genes involved in pH adaptation and osmotic adjustment. Genes related to hydrocarbon degradation, aerobic denitrification and potential industrial important enzymes were also identified from the genome. To our knowledge, this is the first report of a genome sequence of a haloalkaliphilic phenol-degrading bacterium, which will provide insights into the survival of this bacterium under salt-alkali conditions and the potential for biotechnological applications.


April 21, 2020  |  

RNA sequencing: the teenage years.

Over the past decade, RNA sequencing (RNA-seq) has become an indispensable tool for transcriptome-wide analysis of differential gene expression and differential splicing of mRNAs. However, as next-generation sequencing technologies have developed, so too has RNA-seq. Now, RNA-seq methods are available for studying many different aspects of RNA biology, including single-cell gene expression, translation (the translatome) and RNA structure (the structurome). Exciting new applications are being explored, such as spatial transcriptomics (spatialomics). Together with new long-read and direct RNA-seq technologies and better computational tools for data analysis, innovations in RNA-seq are contributing to a fuller understanding of RNA biology, from questions such as when and where transcription occurs to the folding and intermolecular interactions that govern RNA function.


April 21, 2020  |  

Insights into the bacterial species and communities of a full-scale anaerobic/anoxic/oxic wastewater treatment plant by using third-generation sequencing.

For the first time, full-length 16S rRNA sequencing method was applied to disclose the bacterial species and communities of a full-scale wastewater treatment plant using an anaerobic/anoxic/oxic (A/A/O) process in Wuhan, China. The compositions of the bacteria at phylum and class levels in the activated sludge were similar to which revealed by Illumina Miseq sequencing. At genus and species levels, third-generation sequencing showed great merits and accuracy. Typical functional taxa classified to ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), denitrifying bacteria (DB), anaerobic ammonium oxidation bacteria (ANAMMOXB) and polyphosphate-accumulating organisms (PAOs) were presented, which were Nitrosomonas (1.11%), Nitrospira (3.56%), Pseudomonas (3.88%), Planctomycetes (13.80%), Comamonadaceae (1.83%), respectively. Pseudomonas (3.88%) and Nitrospira (3.56%) were the most predominating two genera, mainly containing Pseudomonas extremaustralis (1.69%), Nitrospira defluvii (3.13%), respectively. Bacteria regarding to nitrogen and phosphorus removal at species level were put forward. The predicted functions proved that the A/A/O process was efficient regarding nitrogen and organics removal. Copyright © 2019 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.


April 21, 2020  |  

Genomic analysis of Marinobacter sp. NP-4 and NP-6 isolated from the deep-sea oceanic crust on the western flank of the Mid-Atlantic Ridge

Two Marinobacter sp. NP-4 and NP-6 were isolated from a deep oceanic basaltic crust at North Pond, located at the western flank of the Mid-Atlantic Ridge. These two strains are capable of using multiple carbon sources such as acetate, succinate, glucose and sucrose while take oxygen as a primary electron acceptor. The strain NP-4 is also able to grow anaerobically under 20?MPa, with nitrate as the electron acceptor, thus represents a piezotolerant. To explore the metabolic potentials of Marinobacter sp. NP-4 and NP-6, the complete genome of NP-4 and close-to-complete genome of NP-6 were sequenced. The genome of NP-4 contains one chromosome and two plasmids with the size of 4.6?Mb in total, and with average GC content of 57.0%. The genome of NP-6 is 4.5?Mb and consists of 6 scaffolds, with an average GC content of 57.1%. Complete glycolysis, citrate cycle and aromatics compounds degradation pathways are identified in genomes of these two strains, suggesting that they possess a heterotrophic life style. Additionally, one plasmid of NP-4 contains genes for alkane degradation, phosphonate ABC transporter and cation efflux system, enabling NP-4 extra surviving abilities. In total, genomic information of these two strains provide insights into the physiological features and adaptation strategies of Marinobacter spp. in the deep oceanic crust biosphere.


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