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Asset Tag: CCS

May 16, 2022  |  Gene therapy + editing

Application brochure — AAV Sequencing with HiFi Reads

With Single Molecule, Real-Time (SMRT®) sequencing on the Sequel® IIe systems, you can sequence AAV
genome populations to identify truncation, mutation, and host integration events. The AAV workflow from
PacBio® accommodates both scAAV and ssAAV constructs with easy on-instrument HiFi read generation

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June 1, 2021

Highly sensitive, non-invasive detection of colorectal cancer mutations using single molecule, third generation sequencing.

Colorectal cancer (CRC) represents one of the most prevalent and lethal malignant neoplasms and every individual of age 50 and above should undergo regular CRC screening. Currently, the most effective procedure to detect adenomas, the precursors to CRC, is colonoscopy, which reduces CRC incidence by 80%. However, it is an invasive approach that is unpleasant for the patient, expensive, and poses some risk of complications such as colon perforation. A non-invasive screening approach with detection rates comparable to those of colonoscopy has not yet been established. The current study applies Pacific Biosciences third generation, single molecule sequencing to the inspection of CRC-driving mutations. Our approach combines the screening power and the extremely high accuracy of circular consensus (CCS) third generation sequencing with the non-invasiveness of using stool DNA to detect CRC-associated mutations present at extremely low frequencies and establishes a foundation for a non-invasive, highly sensitive assay to screen the population for CRC and early stage adenomas. We performed a series of experiments using a pool of fifteen amplicons covering the genes most frequently mutated in CRC (APC, Beta Catenin, KRAS, BRAF, and TP53), ensuring a theoretical screening coverage of over 97% for both CRC and adenomas. The assay was able to detect mutations in DNA isolated from stool samples from patients diagnosed with CRC at frequencies below 0.5 % with no false positives. The mutations were then confirmed by sequencing DNA isolated from the excised tumor samples. Our assay should be sensitive enough to allow the early identification of adenomatous polyps using stool DNA as analyte. In conclusion, we have developed an assay to detect mutations in the genes associated with CRC and adenomas using Pacific Biosciences RS Single Molecule, Real Time Circular Consensus Sequencing (SMRT-CCS). With no systematic bias and a much higher raw base-calling quality (CCS) compared to other sequencing methods, the assay was able to detect mutations in stool DNA at frequencies below 0.5 % with no false positives. This level of sensitivity should be sufficient to allow the detection of most adenomatous polyps using stool DNA as analyte, a feature that would make our approach the first non-invasive assay with a sensitivity comparable to that of colonoscopy and a strong candidate for the non-invasive preventive CRC screening of the general population.

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June 1, 2021

Profiling metagenomic communities using circular consensus and Single Molecule, Real-Time Sequencing.

There are many sequencing-based approaches to understanding complex metagenomic communities spanning targeted amplification to whole-sample shotgun sequencing. While targeted approaches provide valuable data at low sequencing depth, they are limited by primer design and PCR amplification. Whole-sample shotgun experiments generally use short-read, second-generation sequencing, which results in data processing difficulties. For example, reads less than 1 kb in length will likely not cover a complete gene or region of interest, and will require assembly. This not only introduces the possibility of incorrectly combining sequence from different community members, it requires a high depth of coverage. As such, rare community members may not be represented in the resulting assembly. Circular-consensus, single molecule, real-time (SMRT) Sequencing reads in the 1-2 kb range, with >99% accuracy can be efficiently generated for low amounts of input DNA. 10 ng of input DNA sequenced in 4 SMRT Cells would generate >100,000 such reads. While throughput is low compared to second-generation sequencing, the reads are a true random sampling of the underlying community, since SMRT Sequencing has been shown to have no sequence-context bias. Long read lengths mean that that it would be reasonable to expect a high number of the reads to include gene fragments useful for analysis.

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June 1, 2021

Analysis of full-length metagenomic 16S genes by Single Molecule, Real-Time Sequencing

High-throughput sequencing of the complete 16S rRNA gene has become a valuable tool for characterizing microbial communities. However, the short reads produced by second-generation sequencing cannot provide taxonomic classification below the genus level. In this study, we demonstrate the capability of PacBio’s Single Molecule, Real-Time (SMRT) Sequencing to generate community profiles using mock microbial community samples from BEI Resources. We also evaluate multiplexing capabilities using PacBio barcodes on pooled samples comprising heterogeneous 16S amplicon populations representing soil, fecal, and mock communities.

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June 1, 2021

Profiling metagenomic communities using circular consensus and Single Molecule, Real-Time Sequencing

There are many sequencing-based approaches to understanding complex metagenomic communities, spanning targeted amplification to whole-sample shotgun sequencing. While targeted approaches provide valuable data at low sequencing depth, they are limited by primer design and PCR amplification. Whole-sample shotgun experiments require a high depth of coverage. As such, rare community members may not be represented in the resulting assembly. Circular-consensus, Single Molecule, Real-Time (SMRT) Sequencing reads in the 1-2 kb range, with >99% consensus accuracy, can be efficiently generated for low amounts of input DNA, e.g. as little as 10 ng of input DNA sequenced in 4 SMRT Cells can generate >100,000 such reads. While throughput is low compared to second-generation sequencing, the reads are a true random sampling of the underlying community. Long read lengths translate to a high number of the reads harboring full genes or even full operons for downstream analysis. Here we present the results of circular-consensus sequencing on a mock metagenomic community with an abundance range of multiple orders of magnitude, and compare the results with both 16S and shotgun assembly methods. We show that even with relatively low sequencing depth, the long-read, assembly-free, random sampling allows to elucidate meaningful information from the very low-abundance community members. For example, given the above low-input sequencing approach, a community member at 1/1,000 relative abundance would generate 100 1-2 kb sequence fragments having 99% consensus accuracy, with a high probability of containing a gene fragment useful for taxonomic classification or functional insight.

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June 1, 2021

Profiling the microbiome in fecal microbiota transplantation using circular consensus and Single Molecule, Real-Time Sequencing

There are many sequencing-based approaches to understanding complex metagenomic communities spanning targeted amplification to whole-sample shotgun sequencing. While targeted approaches provide valuable data at low sequencing depth, they are limited by primer design and PCR. Whole-sample shotgun experiments generally use short-read sequencing, which results in data processing difficulties. For example, reads less than 500bp in length will rarely cover a complete gene or region of interest, and will require assembly. This not only introduces the possibility of incorrectly combining sequence from different community members, it requires a high depth of coverage. As such, rare community members may not be represented in the resulting assembly. Circular-consensus, single molecule, real-time (SMRT®) Sequencing reads in the 1-3kb range, with >99% accuracy can be efficiently generated for low amounts of input DNA. 10 ng of input DNA sequenced in 4 SMRT Cells on the PacBio RS II would generate >100,000 such reads. While throughput is lower compared to short-read sequencing methods, the reads are a true random sampling of the underlying community since SMRT Sequencing has been shown to have very low sequence-context bias. With reads >1 kb at >99% accuracy it is reasonable to expect a high percentage of reads include gene fragments useful for analysis without the need for de novo assembly. Here we present the results of circular consensus sequencing for an individual’s microbiome, before and after undergoing fecal microbiota transplantation (FMT) in order to treat a chronic Clostridium difficile infection. We show that even with relatively low sequencing depth, the long-read, assembly-free, random sampling allows us to profile low abundance community members at the species level. We also show that using shotgun sampling with long reads allows a level of functional insight not possible with classic targeted 16S, or short read sequencing, due to entire genes being covered in single reads.

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June 1, 2021

Minimization of chimera formation and substitution errors in full-length 16S PCR amplification

The constituents and intra-communal interactions of microbial populations have garnered increasing interest in areas such as water remediation, agriculture and human health. One popular, efficient method of profiling communities is to amplify and sequence the evolutionarily conserved 16S rRNA sequence. Currently, most targeted amplification focuses on short, hypervariable regions of the 16S sequence. Distinguishing information not spanned by the targeted region is lost and species-level classification is often not possible. SMRT Sequencing easily spans the entire 1.5 kb 16S gene, and in combination with highly-accurate single-molecule sequences, can improve the identification of individual species in a metapopulation. However, when amplifying a mixture of sequences with close similarities, the products may contain chimeras, or recombinant molecules, at rates as high as 20-30%. These PCR artifacts make it difficult to identify novel species, and reduce the amount of productive sequences. We investigated multiple factors that have been hypothesized to contribute to chimera formation, such as template damage, denaturing time before and during cycling, polymerase extension time, and reaction volume. Of the factors tested, we found two major related contributors to chimera formation: the amount of input template into the PCR reaction and the number of PCR cycles. Sequence errors generated during amplification and sequencing can also confound the analysis of complex populations. Circular Consensus Sequencing (CCS) can generate single-molecule reads with >99% accuracy, and the SMRT Analysis software provides filtering of these reads to >99.99% accuracies. Remaining substitution errors in these highly-filtered reads are likely dominated by mis-incorporations during amplification. Therefore, we compared the impact of several commercially-available high-fidelity PCR kits with full-length 16S amplification. We show results of our experiments and describe an optimized protocol for full-length 16S amplification for SMRT Sequencing. These optimizations have broader implications for other applications that use PCR amplification to phase variations across targeted regions and to generate highly accurate reference sequences.

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June 1, 2021

SMRT Sequencing for the detection of low-frequency somatic variants

The sensitivity, speed, and reduced cost associated with Next-Generation Sequencing (NGS) technologies have made them indispensable for the molecular profiling of cancer samples. For effective use, it is critical that the NGS methods used are not only robust but can also accurately detect low frequency somatic mutations. Single Molecule, Real-Time (SMRT) Sequencing offers several advantages, including the ability to sequence single molecules with very high accuracy (>QV40) using the circular consensus sequencing (CCS) approach. The availability of genetically defined, human genomic reference standards provides an industry standard for the development and quality control of molecular assays. Here we characterize SMRT Sequencing for the detection of low-frequency somatic variants using the Quantitative Multiplex DNA Reference Standard from Horizon Diagnostics, combined with amplification of the variants using the Multiplicom Tumor Hotspot MASTR Plus assay. The Horizon Diagnostics reference sample contains precise allelic frequencies from 1% to 24.5% for major oncology targets verified using digital PCR. It recapitulates the complexity of tumor composition and serves as a well-characterized control. The control sample was amplified using the Multiplicom Tumor Hotspot Master Plus assay that targets 252 amplicons (121-254 bp) from 26 relevant cancer genes, which includes all 11 variants in the control sample. The amplicons were sequenced and analyzed using SMRT Sequencing to identify the variants and determine the observed frequency. The random error profile and high accuracy CCS reads make it possible to accurately detect low frequency somatic variants.

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June 1, 2021

An improved circular consensus algorithm with an application to detection of HIV-1 Drug-Resistance Associated Mutations (DRAMs)

Scientists who require confident resolution of heterogeneous populations across complex regions have been unable to transition to short-read sequencing methods. They continue to depend on Sanger Sequencing despite its cost and time inefficiencies. Here we present a new redesigned algorithm that allows the generation of circular consensus sequences (CCS) from individual SMRT Sequencing reads. With this new algorithm, dubbed CCS2, it is possible to reach arbitrarily high quality across longer insert lengths at a lower cost and higher throughput than Sanger Sequencing. We apply this new algorithm, dubbed CCS2, to the characterization of the HIV-1 K103N drug-resistance associated mutation, which is both important clinically, and represents a challenge due to regional sequence context. A mutation was introduced into the 3rd position of amino acid position 103 (A>C substitution) of the RT gene on a pNL4-3 backbone by site-directed mutagenesis. Regions spanning ~1,300 bp were PCR amplified from both the non-mutated and mutant (K103N) plasmids, and were sequenced individually and as a 50:50 mixture. Sequencing data were analyzed using the new CCS2 algorithm, which uses a fully-generative probabilistic model of our SMRT Sequencing process to polish consensus sequences to arbitrarily high accuracy. This result, previously demonstrated for multi-molecule consensus sequences with the Quiver algorithm, is made possible by incorporating per-Zero Mode Waveguide (ZMW) characteristics, thus accounting for the intrinsic changes in the sequencing process that are unique to each ZMW. With CCS2, we are able to achieve a per-read empirical quality of QV30 with 19X coverage. This yields ~5000 1.3 kb consensus sequences with a collective empirical quality of ~QV40. Additionally, we demonstrate a 0% miscall rate in both unmixed samples, and estimate a 48:52% frequency for the K103N mutation in the mixed sample, consistent with data produced by orthogonal platforms.

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