DRISEE: Duplicate Read Inferred Sequencing Error Estimation
Contributors: Kevin Keegan, William Trimble, Jared Wilkening, Andreas Wilke, Travis Harrison, Mark D'souza, & Folker Meyer
DRISEE is a tool that utilizes artifactual duplicate reads (ADRs) to provide a platform independent assessment of sequencing error in metagenomic (or genomic) sequencing data. DRISEE is designed to consider shotgun data. Currently, it is not appropriate for amplicon data.
A Unix environment ( Unix / Linux / OSX / Darwin / Cygwin / etc. ) DRISEE was developed to run on multicore Unix systems, but can be run on a desktop or laptop. DRISEE has been run on several OSX based systems.
- perl 5.12.1 or later (http://www.perl.org/get.html) *1
- python 2.6 or later (http://python.org/getit/) with biopython (http://biopython.org/wiki/Biopython) *1
- QIIME and the supporting uclust packages (http://qiime.org/install/virtual_box.html) *1
- cdbfasta & cdbyank (http://sourceforge.net/projects/cdbfasta/) *1
*1 Please note that users are responsible for making sure that their use of required software products is compliant with existing licenses and/or user agreements.
Download and place the four script files (listed below) into your folder of choice.
A location in your exisiting PATH makes the most sense; alternatively, you can add the selected folder to your exisiting PATH.
drisee.py (the main driving script - a main script file) seq_length_stats.py (an accessory script - generates sequence related stats) run_find_steiner.pl (an accessory script - performs iterative consensus sequence construction) qiime-uclust (an accessory script - runs qiime-integrated uclust)
DRISEE utilizes three scripts to perform its analyses. All options and input parameters are passed to the main script (drisee.py) which calls the other scripts as needed. Each of the options and input parameters are explained below. Examples of a typical execution are provided further below:
drisee.py [options] input_seq_file output_stat_file_pattern
Input: fasta/fastq file (input_seq_file) Output: error matrix file(s) (output_stat_file_pattern) STDOUT: Runtime summary stats
--version show the DRISEE version number -h, --help show help/usage and exit -p PROCESSES, --processes=PROCESSES [default '1'] Number of processes to use. With this option you can select the number of processers to use on a multiprocessor system. When more than 1 processor is selected, processing of bins of duplicate reads is split among the specified number of processors. -t SEQ_TYPE, --seq_type=SEQ_TYPE [default 'fasta'] Sequence type: fasta, fastq Specify the type of sequence file; fasta and fastq are the only accepted options -f, --filter_seq [default True] Run sequence filtering, Sequence filtering performs two filtering processes before data are processed. (1) An average and standard deviation is determined for the lengths of all reads. The standard deviation is multiplied by the standard deviation multiplier (option -m STDEV_MULTI below). The product of this multiplication is added or subtracted to the average sequence length to determine upper and lower bounds for sequence length. All reads with a length greater than the upper bound, or less than the lower bound, are excluded from analysis. (2) Each remaining read is screened for ambiguous bases ("N"). Reads with that possess a number of ambiguous bases that matches or exceeds the specified limit (see -a AMBIG_MAX below)with -a AMBIG_MAX are excluded from further analysis. -r REP_FILE, --replicate_file=REP_FILE[default to calculate replicates] List file with sorted indices for replicate bins. The file has one row for each read: two columns indicating the bin and sequence id for the read -d TMPDIR, --tmp_dir=TMPDIR [default '/tmp'] Directory for intermediate files (must be full path), deleted at the end of analysis. -l LOGFILE, --log_file=LOGFILE [default '/dev/null'] A detailed log of processing related statistics --percent [default True] Produce second output profile with values presented as percent per position. Additional output file is named "output_stat_file_pattern".per --prefix_length=PREFIX [default 50] Prefix length for the identification of bins of ADRs -s SEQ_MAX, --seq_max=SEQ_MAX [default 10000000] Maximum number of reads to process. The specified number of reads are randomly selected from the input fasta/fastq. The remaining reads are excluded from analysis. It is frequently possible to determine the DRISEE error for a data set using less than the total number of reads. However; to validate your sample size, it is recommended that you perform DRISEE with a number of different sample sizes. Make sure that your sample size is large enough not to be affected by stochastic sampling artifacts (i.e. that multiple iterations run at the selected sample size produce the same result. -a AMBIG_MAX, --ambig_bp_max=AMBIG_MAX [default 0] Maximum number of ambiguous bases ("N") allowed per read before the read is rejected. Note that inclusion of even a single ambiguous character can dramatically affect multiple sequence alignments of bins of prefix-identical bins. We recommend exclusion of reads that contain any ambiguous bases. -m STDEV_MULTI, --stdev_multiplier=STDEV_MULTI [default 2.0] Multiplier by which the standard deviation in the length of the input reads is multiplied to establish upper and lower bounds for length based read filtering (see -f, --filter_seq) -n READ_MIN, --bin_read_min=READ_MIN [default 20] Minimum number of reads a bin of prefix identical reads must possess for it to be considered in the error calculations -x READ_MAX, --bin_read_max=READ_MAX [default 1000] Maximum number of reads to process from each bin of prefix identical reads. We have found that values much smaller than 1000 can lead to stochastic artifacts. Consideration of more reads is possible, but in our testing, rarely leads to results that are appreciably different from those determined from the default of 1000 reads. This parameter also always for informal control of bin weighting; no bin is allowed to contribute more than 1000 reads to the error calculation (i.e.) exceptionally large bins are not allowed to dominate error calculations. Reads are randomly selected. -b NUM_MAX, --bin_num_max=NUM_MAX [default 1000] Maximum number of prefix bins to process. Bins of prefix identical reads are randomly selected. Analyses that consider smaller numbers of bins are more prone to stochastic artifacts. Those that consider larger numbers of bins rarely lead to results that differ appreciably from those determined from a default selection of 1000 bins. -i ITER_MAX, --iter_max=ITER_MAX [default 10] In the multiple alignment step (used to generate the consensus sequence for each bin of prefix identical reads), specifies the maximum number of iterations to perform if convergence (convergence = no change in cluster identity over at least CONV_MIN iterations, see below) is not achieved. In our analysis, bins that require more than 2-3 iterations are exceptionally rare, and usually indicate the presence of ambiguous bases or highly inconsistent sequence content in the non-prefix portion of the reads. -c CONV_MIN, --converge_min=CONV_MIN [default 3] Minimum number of iterations to identify convergence. Multiple alignments are iterated until convergence is observed for CONV_MIN consecutive iterations, or when ITER_MAX (see above) has been reached. -v, --verbose [default off] Write runtime summary stats to STDOUT
Example command line
(1)> drisee.py my_fasta my_fasta.err # will use all default settings on input fasta file my_fasta # primary output (raw output) will be called my_fasta.err (2)> drisee.py -v -l log test_fasta2 test_fasta2.err # use the verbose setting to get some basic stats # and the log setting to generate a detailed runtime log (3)> drisee.py -p 10 -l example_log -v example_fasta example_fasta.drisee_results > verbose_text & # run drisee with 10 cpus on the example_file (see below), # printing a log and the stdout text
Example input/output files
unzip example_files.zip: This file cotains the following:
example_fasta # an example input fasta file (used for example command line 3 above) example_fasta_results # example of the raw counts format (produced from example command line 3 above) example_fasta_results.per # example of the percentage output (produced from example command line 3 above) example_log # example of the log (produced from example command line 3 above)
DRISEE can produce 2 profile formats, raw counts, and percent per consensus indexed base.
The raw counts output has the following format:
# A_err T_err C_err G_err N_err X_err bp_err # Raw counts 0.096899 0.000000 0.000000 0.000000 0.000000 0.000000 0.096899 # A T C G N X A T C G N X 1 0 0 24 0 0 0 0 0 0 0 0 0 2 0 0 0 24 0 0 0 0 0 0 0 0 3 24 0 0 0 0 0 0 0 0 0 0 0 4 0 24 0 0 0 0 0 0 0 0 0 0 ...
The first line ("A_err T_err ...") contains headers for the summary values. It also also
indicates the length of the prefix ("prefix_length") used for a given DRISEE analysis.
Here a 50 base-long prefix was used.
The second line values indicate the various error rates (described below)calculated from the non-prefix portion of the reads that have undergone DRISEE analysis. A, T, C, & G_err indicate the A, T, C & G substituation rates respectively. N_err indicates the substitution rate for ambiguous base calls - by default reads that contain ambiguous base calls are exceluded from DRISEE analysis (Keegan et. al. 2012); reads with ambiguous bases can be included in analyses if non default parameters are used. X_err indicates the combined insertion/deletion error rate rate bp_err indicates the total error, the sum of A, T, C, G, N, & X _err.
The third line contains headers for the DRISEE raw counts.
The columns labeled as "A, T, C, G, C, X, A, T, C, G, C, X" represent (in order from left to right)
A: bases that match consensus
T: bases that match consensus
C: bases that match consensus
G: bases that match consensus
N: ambiguous bases that match consensus
X: insertion or deletions that match consensus
A: bases that do not match consensus
T: bases that do not match consensus C: bases that do not match consensus G: bases that do not match consensus N: ambiguous bases that do not match consensus X: insertion or deletions that do not match consensus
The fourth line ("1 0 0 24 0 ...") indicates the integer counts for the match or mismatches described in third line header, for the first position for all consideredbins of prefix identical reads. The fifth line indicates the same information for the second position in all considered bins of prefix identical reads etc. This format extends to the end of the file. The example above includes the count data for the first 5 bases - as these are part of the 50 base long prefix region, they are expected to be identical -- all displayed counts correspond to consensus matches.
The percentage output has the following format:
# A_err T_err C_err G_err N_err X_err bp_err # Percent counts 0.096899 0.000000 0.000000 0.000000 0.000000 0.000000 0.096899 # A T C G N X A T C G N X 1 0.000000 0.000000 100.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 2 0.000000 0.000000 0.000000 100.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 3 0.000000 0.000000 100.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 4 0.000000 0.000000 0.000000 100.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 ...
This is similar to the format for the raw output. The summary header and summary values are identical to those from the raw counts file.
Lines 4 on are produced from the the values used to generate the raw output. These are modified as follows: each row presents counts as the percent of total counts for that row (i.e. for the indicated seqeunce-indexed postion). In the example above, the row indexed as "1" has a value of 100 under the first "C" column, indicating that 100% of considered reads match a consensus "C" at postion 1. A value of "0" in the second "C" column indicates that no reads possess a "C" at this postion that does not match their respective consensus sequence. These values are calculated from the corresponding counts in the raw counts output: a value of "24" for the first "C" column (percent = 24/24*100), and "0" for the second "C" column (percent = 0/24). Where 24 is the number of total counts (in this example it is also the number of "C" counts that match their consensus at postion 1). .
See Keegan 2012 (email kkeegan AT anl.gov :: manuscript is currently under review) for more details.
PLOTTING DRISEE OUTPUTS
Two scripts allow you to produce linear graphs from *.DRISEE (raw DRISEE abundance output) and *.DRISEE.per (percentage scaled DRISEE output) outputs. One is an independent R script (plot_DRISEE.11-19-12.r), the second is a shell script (plot_DRISEE_shell.sh) -- the shell script is a shell wrapper for the R script. Usage information for each plotting script is provided in the script/ script usage.
This is DRISEE version 1.2 (April 2012)
- Debugged 11-13-12
- Added plotting scripts 11-19-12
Keegan KP, Trimble WL, Wilkening J, Wilke A, Harrison T, et al. (2012) A Platform-Independent Method for Detecting Errors in Metagenomic Sequencing Data: DRISEE. PLoS Comput Biol 8(6): e1002541. doi:10.1371/journal.pcbi.1002541
DRISEE was designed to run on a Unix platform, preferably with access to multiple processors.
A typical DRISEE analysis using the default parameters specified above takes on the order of 10's of minutes to a few hours to complete. Processing time will vary considerably based on the size of the input data file. DRISEE has been run on OSX machines with a single CPU; processing times are generally longer, based largely on the limited capability of such machines to perform parallel computation on multiple CPUs.
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