BOL: Related items

QuorUM: An Error Corrector for Illumina Reads

Jit — Wed, 08 Nov 2017 11:40:41 -0600

Illumina Sequencing data can provide high coverage of a genome by relatively short (most often 100 bp to 150 bp) reads at a low cost. Even with low (advertised 1%) error rate, 100 × coverage Illumina data on average has an error in some read at every base in the genome. These errors make handling the data more complicated because they result in a large number of low-count erroneous k-mers in the reads. However, there is enough information in the reads to correct most of the sequencing errors, thus making subsequent use of the data (e.g. for mapping or assembly) easier. Here we use the term “error correction” to denote the reduction in errors due to both changes in individual bases and trimming of unusable sequence. We developed an error correction software called QuorUM. QuorUM is mainly aimed at error correcting Illumina reads for subsequent assembly. It is designed around the novel idea of minimizing the number of distinct erroneous k-mers in the output reads and preserving the most true k-mers, and we introduce a composite statistic π that measures how successful we are at achieving this dual goal. We evaluate the performance of QuorUM by correcting actual Illumina reads from genomes for which a reference assembly is available.

QuorUM is distributed as an independent software package and as a module of the MaSuRCA assembly software. Both are available under the GPL open source license at http://www.genome.umd.edu.

Address of the bookmark: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0130821

Common steps for reads mapping !

BioStar — Thu, 09 Mar 2023 02:48:02 -0600

Mapping reads to a reference genome is an essential step in many types of genomic analysis, such as variant calling and gene expression analysis. Here are some general steps to follow for mapping reads to a genome:

Choose a read mapper: There are many read mappers available, such as BWA, Bowtie, and HISAT2. Choose a mapper that is appropriate for your type of data and research question.
Index the reference genome: Before mapping reads, the reference genome needs to be indexed. This involves creating an index of the genome sequence that allows the mapper to quickly find matches to the reads. Most mappers have their own indexing tools.
Prepare the read data: The reads should be in a format that is compatible with the mapper. Most mappers accept FASTQ or BAM files. Depending on the quality of the data, it may need to be filtered or trimmed before mapping.
Run the mapper: The mapper is run with the command-line interface or using a graphical user interface. The specific command depends on the mapper being used, but typically involves specifying the input data, reference genome, and output file format.
Evaluate the mapping results: After the mapping is complete, the results should be evaluated. This includes assessing the quality of the mapping, such as the mapping rate, the number of mapped reads, and the mapping quality score.
Post-processing: Depending on the analysis being performed, post-processing of the mapped reads may be necessary. This can include filtering reads based on quality, removing duplicate reads, and calling variants.

Overall, mapping reads to a reference genome is a complex process that requires careful consideration of the type of data, the research question, and the specific mapper being used.

Simulating the Unseen: New Tools Reshaping Metagenomic Research

LEGE — Wed, 23 Sep 2026 09:42:30 -0500

When benchmarking a new metagenomic pipeline the first step is generally to face a simple problem. A bioinformatician might have a good deal of real sequencing data, but there's a drawback in that the actual biological composition underlying those reads is almost never known. What organisms really were there? In what quantities? How many sequencing errors occurred? Can the pipeline correctly reconstruct the community? Since the true answers are unknown, it is difficult to deal with these questions.

Metagenomic simulators are a way of dealing with this issue; they produce artificial sequencing datasets in which both the composition of the microorganisms and the expected results are known. Researchers can then test a pipeline on such a controlled dataset and see precisely how well it functions. However, as metagenomic studies have become larger, more diverse, and more complex, simply generating artificial reads is no longer sufficient. The simulators now have to replicate community variation, sequencing errors, different sequencing platforms, massive data volumes, and even laboratory-based biases.

MIDASim (2024) was designed with a particular emphasis on microbial community dynamics. Unlike previous tools which regarded each simulated sample as individual, MIDASim is able to efficiently generate realistic multi-sample microbiome datasets, covering the cases where changes over time are being tracked. This feature is particularly useful when investigating how microbial communities vary between people, different experimental setups, or at various times. By overcoming the computational limitations of earlier simulation methods, MIDASim has made it easier to carry out large and complex microbiome simulation studies.

A major challenge is scale. Since modern metagenomic projects can involve millions or even billions of sequencing reads, generating such large synthetic datasets can become a significant computational problem. In order to tackle this issue, Izzy (2025) was developed. As a high-throughput metagenomic read simulator, Izzy is designed with speed in mind while still reproducing the typical patterns of sequencing errors. The people who developed it stated that it can be as much as 60 times faster than earlier tools, which makes large-scale simulations far more practical. Now, researchers can begin to ask not how long a simulation will take but rather what size dataset they want to test.

At the same time, the sequencing technology became more diverse. Researchers were not any longer restricted to using Illumina short reads since Oxford Nanopore and PacBio long-read sequencing also became important in the field of metagenomic research. In order to address these new requirements, MeSS (Metagenomic Sequence Simulator, 2025) was developed. The programme is based on a Snakemake framework and is therefore compatible with the Illumina, Oxford Nanopore and PacBio platforms. MeSS has also been designed to operate efficiently and to use less memory than earlier tools; it provides ready-made templates for the microbiomes of different sites in the human body, thus giving researchers a simple means of beginning to generate realistic simulated communities.

The simulation problem became even more specialized. Suppose that sequencing is not based on uniform sampling of DNA? In the case of targeted sequencing and hybridization-capture experiments, particular sequences are deliberately enriched, and the probability of capturing a target depends on both the probe and the target sequence. A standard model based on uniform sampling might fail to take into account this important feature of real experiments. That is why RAmpSim has been designed specifically to handle simulations for capture-based and targeted sequencing. Instead of depending solely on the assumption of uniform sampling, it includes a thermodynamic nearest-neighbor energy model to represent probe–target interactions and sequence-dependent enrichment. As a result, it is especially suitable for applications such as hybridization capture in metagenomics, where the efficiency of recovering a sequence can depend strongly on how it relates to the capture probes. RAmpSim thus reflects a wider trend towards simulations that aim not only to reproduce sequencing output but also key aspects of the experimental process itself.

MIDASim, Izzy, MeSS and RAmpSim all demonstrate how fast metagenomic simulation is evolving. MIDASim is able to deal with realistic variation within a large number of and changing microbial communities. Izzy overcomes the problem of generating very large datasets. MeSS provides support for a number of sequencing technologies in an efficient and repeatable manner. RAmpSim increases the experimental realism for capture-based sequencing. Although each of these tools addresses a separate issue, they all contribute to advancing the field.

Modern metagenomic simulation therefore aims not only at producing artificial FASTQ files. Researchers nowadays desire simulated datasets that reflect community changes, incorporate the characteristics of the sequencing platform, include real error patterns, take into account computational scale, and account for experimental biases. As metagenomic workflows become more advanced, the simulators have to keep up with this development. The tools are now going beyond that of simple data generators; they produce controlled versions of complex metagenomic experiments and thus provide researchers with something that ordinary sequencing data seldom does: a dataset in which the answer is known before any analysis takes place.

Should you get sequenced? Not all bad genes predict disease

Rahul Agarwal — Thu, 29 Aug 2013 15:10:53 -0500

“What we really don’t know yet is whether the predictive aspects of the genome are going to turn out to be beneficial or potentially harmful”

“As we roll out genomic medicine we are fighting against this society-wide misconception that having the bad gene means you’re going to get the disease. That’s only true in a very few cases.”

Source:Today Health

Address of the bookmark: http://www.today.com/health/should-you-get-sequenced-not-all-bad-genes-predict-disease-8C11017154

Barber pole worm , sheep pathogen sequenced !!!

Rahul Agarwal — Tue, 03 Sep 2013 16:32:18 -0500

Haemonchus contortus is a highly pathogenic parasitic nematode of that can infect a large number of wild and domesticated ruminant species and is the most economically important parasite of sheep and goats worldwide. Scientists at the Wellcome Trust Sanger Institute have sequenced the genome of the barber's pole worm (Haemonchus contortus), which will help to explore the this tropical parasite which been disseminated around the world by livestock movement.

H. contortus is a member of the superfamily trichostrongyloidea (Strongylida) which contains most of the economically important parasitic nematodes of grazing livestock. These parasites cost the global livestock industry billions of dollars per annum in lost production and drug costs. A common type of clover may be a preventative or palliative for the disease. However, some particular breeds of sheep, such as the Gulf Coast Native from the Southern United States, have been shown to have developed special resistance to H. contortus.

Getting the full genome can help to tackle the problem and understand the resistance mechanism with an ease. Moreover, the genome could now provide a comprehensive understanding of how treatments against parasitic worms work and point to further new treatments and vaccines. By comparing the genome of the barber's pole worm with those of worms that have acquired drug resistance, researchers expect to reveal information about how and why resistance has occurred. Till now, researchers have uncovered essential information in the fight against drug resistance in worms.

Reference:

http://www.fwi.co.uk/articles/28/08/2013/140758/researchers-close-in-on-worm-resistance-in-sheep.htm

http://www.sciencedaily.com/releases/2013/08/130828103351.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily%2Fplants_animals+(ScienceDaily%3A+Plants+%26+Animals+News)

Image source: Wikipedia

DNA tale of 3 to 4 years old Serbia boy

Rahul Agarwal — Tue, 26 Nov 2013 17:34:00 -0600

The genome of a young boy found underground at Mal’ta near Lake Baikal of eastern Siberia around 24,000 years ago came out as close relative of Europeans and Native Indians.

Link:

http://www.nytimes.com/2013/11/21/science/two-surprises-in-dna-of-boy-found-buried-in-siberia.html?_r=0

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12736.html

Genome of Rainbow Trout Sequenced

Rahul Agarwal — Fri, 25 Apr 2014 10:36:51 -0500

Major finding:

“In humans and most vertebrates the duplication events were older so there are fewer duplicated genes still present. Most of the duplicated genes get lost or modified so much that they are no longer recognizable as duplicates over time. In the trout and salmon we can see an earlier stage in the process and many duplicated genes are still present,” said Dr Gary Thorgaard of Washington State University, a co-author of the paper published in the journal Nature Communications.

Source:

http://www.sci-news.com/genetics/science-genome-rainbow-trout-01877.html

Real time Sequencing

Rahul Agarwal — Sun, 04 May 2014 18:16:42 -0500

“... we now know we can do high-throughput sequencing at any location on Earth,” Moroz said.

Source:

http://news.ufl.edu/2014/04/28/real-time-genome-sequencing-at-sea/

miRNA database and tools

Rahul Agarwal — Mon, 09 Jun 2014 07:58:40 -0500

Since few years miRNA has shown to play important role in therapeutic related research and also known to play vital role in controlling gene expression specifically at transcriptional and post-transcription levels. Here are some important DBs and tools related with miRNA:

miRNA Sequencing data analysis : http://tools.genxpro.net/omiras/

miRNApath( R based tool) : http://www.bioconductor.org/packages/release/bioc/html/miRNApath.html

miRWalk DB : http://www.umm.uni-heidelberg.de/apps/zmf/mirwalk/

TargetScanHuman : http://www.targetscan.org/

RNAhybrid : http://bibiserv.techfak.uni-bielefeld.de/rnahybrid/welcome.html

RNA22 predictor : http://cbcsrv.watson.ibm.com/rna22.html

miRNA predictor : http://www.microrna.org/microrna/home.do

Plant miRNA DB :http://bioinformatics.cau.edu.cn/PMRD/

miRBASE DB: http://www.mirbase.org/

Plant RNA predictor : http://plantgrn.noble.org/psRNATarget/

miRNA Interaction DB : http://starbase.sysu.edu.cn/

Sequencing based miRNA DB : http://mirgator.kobic.re.kr/

predicted A-to-I edited miRNA DB : http://microrna.osumc.edu/mireditar/

Animal, plant and virus miRNA DB : http://lemur.amu.edu.pl/share/php/mirnest/

Atlantic Salmon miRNAs DB : http://www.molgenv.com/ssa_mirnas_db_home.php

miRNA prediction on UTRs : http://genie.weizmann.ac.il/pubs/mir07/mir07_prediction.html

Idea of analysing miRNA Sequencing data :

http://www.illumina.com/applications/epigenetics/small_rna_analysis.ilmn

More:

http://www.bioconductor.org/help/search/index.html?q=miRNA+target

Scaffolding of a bacterial genome using MinION nanopore sequencing

Rahul Agarwal — Tue, 07 Jul 2015 16:59:25 -0500

Second generation sequencing has revolutionized genomic studies. However, most genomes contain repeated DNA elements that are longer than the read lengths achievable with typical sequencers, so the genomic order of several generated contigs cannot be easily resolved. A new generation of sequencers offering substantially longer reads is emerging, notably the Pacific Biosciences (PacBio) RS II system and the MinION system, released in early 2014 by Oxford Nanopore Technologies through an early access program.

Address of the bookmark: http://www.nature.com/srep/2015/150707/srep11996/full/srep11996.html