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# Platform
Quorum has been tested on Linux with gcc 4.4 to gcc 4.7.
# Installation
You should download the latest release distribution tar ball from the
[releases section](https://github.com/gmarcais/Quorum/releases). If
compiling from the github tree code, you will need `autoconf`,
`automake` and `yaggo`. You can download `yaggo` from the
[github release page](https://github.com/gmarcais/yaggo/releases) and
copy the `yaggo` problem into your `PATH`.
Quorum requires [Jellyfish](https://github.com/gmarcais/Jellyfish/releases) to be installed.
For Quorum to compile `pkg-config` must find Jellyfish. The following command must pring "OK":
~~~
pkg-config --exists jellyfish-2.0 && echo OK
~~~
If not, set the variable `PKG_CONFIG_PATH` appropriately.
If installing from the github tree, first run `autoreconf -fi`. Then
install the usual way:
~~~
./configure --prefix=/path/where/to/install
make
make install
~~~
The last command may need to be run as root, if installing in a system directory.
# Usage
Only one switch (`-s`) is required to run Quorum. This switch specify
the size of the Jellyfish hash and it must be large enough so that all
k-mers will fit into memory. With Illumina reads, a good estimate for
this size is:
(G + k * n) / 0.8
where G is the estimated genome size, k is the k-mer length (24 by
default) and n is the number of reads. If the chosen size is too
small, quorum will stop with the error message: "Failed: Increase the
size parameter".
For example, for a bacteria with 2 million Illumina reads in files
read1.fastq and read2.fastq, the command would be:
~~~
quorum -s 50M read1.fastq read2.fastq
~~~
The output corrected file is called by default `quorum_corrected.fa`.
#Output format
The correction made are appended to the header line in the fasta
format. For example, the following 101 bases long read:
~~~
@1204
GACCGGGCATGGGCTGAGCCTGTTCGGGAAGCTGACGGAGCCGGAAGAGGCCGGGATCGACCCTTCCGCCCCGCCCGCCGACTGGGTCGACCGGCCGGGCG
~~~
is corrected to:
~~~
>1204 86:sub:T-C 91:3_trunc 62:5_trunc
CTTCCGCCCCGCCCGCCGACTGGGCCGAC
~~~
The coordinate system is 0-based in the original reads (like a C or
Perl array). Here, at base 86 a substitution was made from T to C. The
5\_trunc is the index of the first base (0 if not specified) and the
3\_trunc is the index after the last base (read length if not
specified). Hence, the length of the corrected reads is computed as
3\_trunc - 5\_trunc (29 in this example). The uncorrected and corrected
reads align as follows:
~~~
0 62 86 91 101
| | | | |
GACCGGGCATGGGCTGAGCCTGTTCGGGAAGCTGACGGAGCCGGAAGAGGCCGGGATCGACCCTTCCGCCCCGCCCGCCGACTGGGTCGACCGGCCGGGCG
CTTCCGCCCCGCCCGCCGACTGGGCCGAC
~~~
# Switches
Other useful switches include (see `quorum --help` for a short
description of all of them).
* `--threads NUMBER`
Number of threads to use.
* `--kmer-len LENGTH`
Length of k-mer to use. Defaults to 24. This is limited to 31.
* `--contaminant FILE`
Pass in a fasta or fastq file of contaminant sequences. The error
correction program will truncate any reads which contains a k-mer
present in the contaminant sequences.
* `--prefix NAME`
By default, all output file have the form `quorum_*`. This can be
changed with this switch.
* `--min-q-char ASCII`
This is the ASCII value of the base of quality encoding. If not
specified, it is auto-detected: the first 1,000 reads of the first
file are read and the minimum quality value seen in these reads is
used for min-q-char. An error is raised if this auto-detected base is
not one of the standard value (33, 59 or 64).
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