Vol. 28 no. 4 2012, pages 593–594
ART: a next-generation sequencing read simulator
Weichun Huang1,∗, Leping Li1, Jason R. Myers1,†and Gabor T. Marth2,∗
1Biostatistics Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709 and
2Department of Biology, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467, USA
Associate Editor: Martin Bishop
Advance Access publication December 23, 2011
Summary: ART is a set of simulation tools that generate synthetic
next-generation sequencing reads. This functionality is essential for
testing and benchmarking tools for next-generation sequencing data
analysis including read alignment, de novo assembly and genetic
variation discovery. ART generates simulated sequencing reads by
emulating the sequencing process with built-in, technology-specific
read error models and base quality value profiles parameterized
empirically in large sequencing datasets. We currently support
all three major commercial next-generation sequencing platforms:
Roche’s 454, Illumina’s Solexa and Applied Biosystems’ SOLiD.
ART also allows the flexibility to use customized read error model
parameters and quality profiles.
Availability: Both source and binary software packages are available
Contact: firstname.lastname@example.org; email@example.com
Supplementary information: Supplementary data are available at
Received on October 3, 2011; revised on December 6, 2011;
accepted on December 19, 2011
In the past few years, high-throughput next-generation sequencing
wide studies measuring gene expression changes and discovering
genomic/epigenetic variations, and many tools were developed for
analyzing such datasets. Simulated data is indispensable for guiding
tool development and evaluating tool performance, and therefore
it is essential to develop simulation software that can produce
next-generation sequencing reads that captures the most essential
characteristics of real data. Currently available read simulation
programs include Wgsim from the Samtools package (Li et al.,
2009) for generating Illumina sequencing reads, MetaSim (Richter
et al., 2008) for simulating metagenomic data, Mason (http://seqan
.de/projects/mason.html) for both Illumina and 454 reads, SimSeq
(Balzer et al., 2010) for 454 reads. Although these programs
work well in their domain, there is a need for a read simulation
program that can deal with all major sequencing platforms, and
generate sequence reads with both substitution and insertion–
deletion (INDEL) errors, as appropriate for the error modes of each
∗To whom correspondence should be addressed.
†Present address: Department of Biological Sciences, Rochester Institute of
Technology, Rochester, NY 14623, USA.
As a general simulator, our ART software was initially developed
for simulation studies helping to design data collection modalities
of the 1000 Genomes Project (Durbin et al., 2010). ART has
been subsequently used by many users worldwide to facilitate
sequencing software development. ART takes a set of DNA
sequences (representing e.g. a reference genome), and generates
‘synthetic’ sequencing reads in a way that mimics the technology-
specific sequencing process. ART comes with a set of technology-
specific read error profiles, but it can also take user-supplied profiles
to generate sequencing data with customized read length and error
characteristics.ARTcan report simulated reads in the standard SAM
alignment format and UCSC BED files.
ART simulates both single-end and paired-end sequencing reads of
the three main commercial next-generation sequencing platforms:
454, Illumina and SOLiD. The built-in read length and read error
profiles were derived from large sets of actual real sequencing
data (see Supplementary Material). ART supports all three types
of common sequencing errors: base substitutions, insertions and
FEATURES AND METHODS
Illumina sequencing by synthesis is a base-by-base sequencing
technology using a reversible terminator-based method, enabling
detection of single bases as they are incorporated into growing
DNAstrands complementary to the template (Bentley, 2006). Since
this technology reads out one base at a time, the main error mode
is substitution rather than insertion or deletion. The probability
of a substitution error is determined by the base quality score
associated with the called base. The distribution of base quality
scores is position-dependent: the mean quality score decreases as
a function of increasing base position. ART simulates substitution
errors according to the empirical, position-dependent distribution
of base quality scores, measured in large training datasets. The
base quality score does not directly provide information for INDEL
errors, andARTsimulates insertion and deletion errors directly from
empirical distributions from our training data. The current version
of ART comes with four empirical read quality score distributions,
one for each of four different read lengths: 36, 44, 50 and 75bp.
The built-in insertion and deletion error rates were derived from 35
bp reads aligned with our modifiedACANAalignment tool (Huang
et al., 2006). For paired-end simulation, ART uses two different
quality score distributions and error rates for the first and second
reads, each determined empirically.
Illumina read simulation
Published by Oxford University Press 2012.
W.Huang et al.
Table 1. ART simulation speed. Speed measured for generating 10×
read coverage of human chromosome 17, for 454, Illumina, and SOLiD
Platform Read lengthRunning time (s)Speed (no. of reads/s)
Roche/454 sequencing is a pyrosequencing technology that tests for
the presence of each of the four DNA nucleotides (T, A, C, G) in a
cyclical fashion. All consecutive bases within a homopolymer run
signal that is proportional with the number of incorporated bases
(Margulies et al., 2005). The dominant error mode is base over- or
under-call, resulting in INDEL type errors. While sequencing error
rate only slightly increases with the number of flow cycles, the error
rate increases dramatically with the frequency of long homopolymer
homopolymer length-dependent over-call (insertion) and under-call
(deletion) error distributions, and models base quality profiles as
homopolymer length-dependent first-order Markov chains. ART
uses an empirical distribution of 454 read lengths. By default, ART
generates 454 reads with built-in distributions derived for the 454
GS FLX sequencer model.
454 read simulation
Applied Biosystems’ SOLiD sequencing technology is based on
ligation of oligonucleotides. It uses four fluorescent color dyes
to encode the 16 different dinucleotides, each dye encoding four
dinucleotides. SOLiD performs double interrogation of each base
by combining the four-dye encoding scheme with a sequencing
assay that samples every base (http://www.appliedbiosystems.com/
sequencing.html). Different from either 454 or Illumina technology,
the SOLiD base caller reports nucleotide transition color codes,
rather than nucleotide sequences. Accordingly, ART also generates
SOLiD read simulation
nucleotide transition codes or ‘color-space’ reads. For paired-end
read simulations, a Gaussian distribution is used to model the
distribution of DNA fragment sizes. The built-in empirical error
profiles of SOLiD reads were derived from the read data generated
at Applied Biosystems. ART provides an option to tune sequencing
error rates with a linear scaling factor.
To test ART’s speed, we used human chromosome 17 as reference,
and generated reads representing 10× coverage for each of the
three sequencing platforms. The test was performed on a desktop
system. This procedure took <12 min (Table 1), with Illumina reads
being the fastest and SOLiD reads the slowest.
We would like to thank Dr Heather E. Peckham at Applied
Biosystems for kindly providing SOLiD read error profiles.
Funding: Intramural Research Program of the National Institutes
of Health; National Institute of Environmental Health Sciences
(ES101765); National Human Genome Research Institute, National
Institutes of Health (HG003698 and HG004719 to G.T.M.) in part.
Conflict of interest: none declared.
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