Rapidly extracts SNPs from a multi-FASTA alignment, either with respect to an implicit pseudo-reference or given reference sequence.

• Introduction
• Installation
  • OSX/Linux - from source
  • OSX/Linux - from a release tarball
  • Running the tests
• Usage
  • Example input
  • Example usage
  • Output
• License
• Feedback/Issues
• Citation

Rapidly decreasing genome sequencing costs have led to a proportionate increase in the number of samples used in prokaryotic population studies. Extracting single nucleotide polymorphisms (SNPs) from a large whole genome alignment is now a routine task, but existing tools have failed to scale efficiently with the increased size of studies. These tools are slow, memory inefficient and are installed through non-standard procedures. We present SNP-sites which can rapidly extract SNPs from a multi-FASTA alignment using modest resources and can output results in multiple formats for downstream analysis. SNPs can be extracted from a 8.3 GB alignment file (1,842 taxa, 22,618 sites) in 267 seconds using 59 MB of RAM and 1 CPU core, making it feasible to run on modest computers. It is easy to install through the Debian and Homebrew package managers, and has been successfully tested on more than 20 operating systems. SNP-sites is implemented in C and is available under the open source license GNU GPL version 3.

There are a few ways to install SNP-sites. The simpliest way is using apt (Debian/Ubuntu) or Conda. If you encounter an issue when installing SNP-sites please contact your local system administrator. If you encounter a bug please log it here.

• OSX/Linux - from source
• OSX/Linux - from a release tarball

This is a difficult method and is only suitable for someone with advanced unix skills. No support is provided with this method, since you have advanced unix skills. First install a standard development environment (e.g. gcc, automa
ke, autoconf, libtool). Download the software from GitHub.

autoreconf -i -f
./configure
make
sudo make install

This is a difficult method and is only suitable for someone with advanced unix skills. No support is provided with this method, since you have advanced unix skills. First install a standard development environment (e.g. gcc, automa
ke, autoconf, libtool).

tar xzvf snp-sites-x.y.z.tar.gz
cd snp-sites-x.y.z
./configure
make
sudo make install

The test can be run from the top level directory:

autoreconf -i
./configure
make
make check

This requires libcheck (the check package in Ubuntu) to be installed.

Usage: snp-sites [-mvph] [-o output_filename] <file>
This program finds snp sites from a multi fasta alignment file.
 -r     output internal pseudo reference sequence
 -m     output a multi fasta alignment file (default)
 -v     output a VCF file
 -p     output a phylip file
 -o STR specify an output filename [STDOUT]
 -R STR specify reference sequence (FASTA)
 -c     only output columns containing exclusively ACGT
 -b     output monomorphic sites, used for BEAST
 -h     this help message
 -V     print version and exit
 <file> input alignment file which can optionally be gzipped

This application takes in a multi fasta alignment, finds all the SNP sites, then outputs the SNP sites in the following formats:

• a multi fasta alignment,
• VCF,
• relaxed phylip format.

For the given input file:

>sample1
AGACACAGTCAC
>sample1
AGACAC----AC
>sample1
AAACGCATTCAN

the output is:

>sample1
GAG
>sample1
GA-
>sample1
AGT

snp-sites my_alignment.aln
snp-sites my_gzipped_alignment.aln.gz

• Multi Fasta Alignment - Similar to the input file but just containing the SNP sites.

• VCF - This contains the position of each SNP in the reference sequence, and the occurrence in each other sample. Can be loaded into Artemis for visualisation.

• Relaxed Phylip format - All the SNP sites in a format for RAxML and other tree building applications.

SNP-sites is free software, licensed under GPLv3.

This software is community supported. Please report any issues to the issues page.

The original software from which this is forked is featured in the publication:

"SNP-sites: rapid efficient extraction of SNPs from multi-FASTA alignments", Andrew J. Page, Ben Taylor, Aidan J. Delaney, Jorge Soares, Torsten Seemann, Jacqueline A. Keane, Simon R. Harris, Microbial Genomics 2(4), (2016)