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Calculate various summary statistics on a multiple sequence alignment

Project description


Alignment manipulation and summary statistics

If you are using this program, please cite this publication:

Borowiec, M.L. 2016. AMAS: a fast tool for alignment manipulation and computing of summary statistics. PeerJ 4:e1660.


You can download this repository zipped (button on the right-hand side of the screen) and use in the amas directory as a stand-alone program or clone it if you have git installed on your system.

If your system doesn't have a Python version 3.4 or newer (AMAS will work under Python 3.0 but you may noy be able to use it with multiple cores), you will need to download and install it. On Linux-like systems (including Ubuntu) you can install it from the command line using

sudo apt-get install python3

To use AMAS as a Python module you can get it with pip from the Python Package Index:

pip install amas

See below for the instructions on how to use this program as a Python module.

Command line interface

AMAS can be run from the command line. Here is the general usage (you can view this in your command line with python3 -h):

usage: AMAS <command> [<args>]

The AMAS commands are:
  concat      Concatenate input alignments
  convert     Convert to other file format
  replicate   Create replicate data sets for phylogenetic jackknife
  split       Split alignment according to a partitions file
  summary     Write alignment summary
  remove      Remove taxa from alignment
  translate   Translate DNA alignment into protein alignment

Use AMAS <command> -h for help with arguments of the command of interest

positional arguments:
  command     Subcommand to run

optional arguments:
  -h, --help  show this help message and exit

To show help for individual commands, use <command> -h or <command> --help.


For every run on the command line you need to specify action with concat, convert, replicate, split, or summary for the input to be processed. Additionally, you need to provide three arguments required for all commands. The order in which the arguments are given does not matter:

  1. input file name(s) with -i (or in long version: --in-files),

  2. format with -f (--in-format),

  3. and data type with -d (--data-type).

The options available for the format are fasta, phylip, nexus (sequential), phylip-int, and nexus-int (interleaved). Data types are aa for protein alignments and dna for nucleotide alignments.

For example:

python3 concat -i gene1.nex gene2.nex -f nexus -d dna

If you have many files that you want to input in one run, you can use multiple cores of your computer to process them in parallel. The summary command supports -c or --cores with which you can specify the number of cores to be used:

python3 summary -f phylip -d dna -i *phy -c 12

In the above, we specified 12 cores. Note that this won't improve computing time if you're working with only one or very few files. The parallel processing is only used for the file parsing step and calculating alignment summaries.

In addition to overall alignment summaries, you can also print statistics calculated on a sequence (taxon) by sequence basis. Use -s or --by-taxon flag to turn it on. AMAS in this mode will print out one file with overall alignment summaries and a file with taxon summaries for each input alignment.

IMPORTANT! AMAS is fast and powerful, but be careful: it assumes you know what you are doing and will not prevent you overwriting a file. It will, however, print out a warning if this has happened. AMAS was also written to work with aligned data and some of the output generated from unaligned sequences won't make sense. Because of computing efficiency AMAS by default does not check if input sequences are aligned. You can turn this option on with -e or --check-align.

Concatenating alignments

For example, if you want to concatenate all DNA phylip files in a directory and all of them have the .phy extension, you can run:

python3 concat -f phylip -d dna -i *phy

By default the output will be written to two files: partitions.txt, containing partitions from which your new alignment was constructed, and concatenated.out with the alignment itself in the fasta format. You can change the default names for these files with -p (--concat-part) and -t (--concat-out), respectively, followed by the desired name. The output format is specified by -u (--out-format) and can also be any of the following: fasta, phylip, nexus (sequential), phylip-int, or nexus-int (interleaved).

Below is a command specifying the concatenated file output format as nexus with -u nexus:

python3 concat -f fasta -d aa -i *fas -u nexus

Alignments to be concatenated need not have identical sets of taxa before processing: the concatenated alignment will be populated with missing data where a given locus is missing a taxon. However, if every file to be concatenated includes only unique names (for example species name plus sequence name: D_melanogaster_NW_001845408.1 in one alignment, D_melanogaster_NW_001848855.1 in other alignment etc.), you will first need to trim those names so that sequences from one taxon have equivalents in all files.
In addition to the name, you can also specify the format of the partitions output file. By default, the format is the following:

AA = 1-605
AK = 606-1200
28S = 1201-1800


python3 concat -f phylip -d dna -i *phy --part-format raxml
DNA, AA = 1-605
DNA, AK = 606-1200
DNA, 28S = 1201-1800


python3 concat -f phylip -d dna -i *phy --part-format nexus
Begin sets;
    charset AA = 1-605;
    charset AK = 606-1200;
    charset 28S = 1201-1800;

Getting alignment statistics

This is an example of how you can summarize two protein fasta alignments by running:

python3 summary -f fasta -d aa -i my_aln.fasta my_aln2.fasta

By default AMAS will write a file with the summary of the alignment in summary.txt. You can change the name of this file with -o or --summary-out. You can also summarize a single or multiple sequence alignments at once.

The statistics calculated include the number of taxa, alignment length, total number of matrix cells, overall number of undetermined characters, percent of missing data, AT and GC contents (for DNA alignments), number and proportion of variable sites, number and proportion of parsimony informative sites, and counts of all characters present in the relevant alphabet.

Converting among formats

To convert all nucleotide fasta files with a .fas extension in a directory to nexus alignments, you could use:

python3 convert -d dna -f fasta -i *fas -u nexus

In the above, the required options are combined with convert command to convert the input files and -u nexus which indicates the output format.

AMAS will not overwrite over input here but will create new files instead, automatically appending appropriate extensions to the input file's name: -out.fas, -out.phy,, -out.nex, or

Splitting alignment by partitions

If you have a partition file, you can split a concatenated alignment and write a file for each partition:

python3 split -f nexus -d dna -i concat.nex -l partitions.txt -u nexus

In the above one input file concat.nex was provided for splitting with split and partitions file partitions.txt with -l (same as --split-by). For splitting you should only use one input and one partition file at a time. This is an example partition file:

  AApos1&2  =  1-604\3, 2-605\3
  AApos3  =  3-606\3
  28SAutapoInDels=7583, 7584, 7587, 7593

If this was the partitions.txt file from the example command above, AMAS would write three output files called concat_AApos1&2.nex, concat_AApos3.nex, and concat_28SautapoInDels.nex. The partitions file will be parsed correctly as long as there is no text prior to the partition name (CHARSET AApos1&2 or DNA, AApos1&2 will not work) and commas separate ranges or individual sites in each partition.

Sometimes after splitting you will have alignments with taxa that have only gaps - or missing data ?. If you want to these to not be included in the output , add -j or --remove-empty to the command line.

Translating a DNA alignment into aligned protein sequences

You can translate a nucleotide alignment to amino acids with AMAS using one of the NCBI translation tables. For example, to correctly translate an insect mitochondrial gene alignment that begins at a second codon position:

python3 translate -f nexus -d dna -i concat.nex --code 5 --reading-frame 2 --out-format phylip

--code and --reading-frame are the same as -b and -k and are both set to 1 (the standard genetic code and the first character of the alignment corresponds to the first codon position) by default. When translating, AMAS will contract gaps - and missing ?, such that --- becomes - in the translated alignment. A warning will be printed if stop codons are found and these are indicated as asterisks * in the output. See translate -h for more info.

Creating replicate data sets

With AMAS you can create concatenated alignments from a proportion of randomly chosen alignments that can be used for, for example, a phylogenetic jackknife analysis. Say you have 1000 phylip files, each containing a single aligned locus, and you want to create 200 replicate phylip alignments, each built from 100 loci randomly chosen from all the input files. You can do this by specifying replicate command and following it with -r or --rep-aln followed by the number of replicates (in this case 200) and number of alignments (100). Remember to supply the output format with -u if you want it to be other than fasta:

python3 replicate -r 200 100 -d dna -f phylip -i *phy -u phylip

Removing taxa/sequences from alignment

It is possible to remove taxa from alignments:

python3 remove -x species1 species2 -d dna -f nexus -i *nex -u nexus-int -g no_species12_ 

The above will process all nexus files in the directory and remove taxa called species1 and species2. The argument -x (the same as --taxa-to-remove) is followed by the names of sequences to be removed. Note that AMAS converts spaces into underscores and strips any quotes present in input sequence names before processing, so you may need to modify your names to remove accordingly. The argument -g (the same as --out-prefix) specifies a prefix to be added to output file names. The default prefix is 'reduced_'. You may want to realign your files after taxon removal.

Checking if input is aligned

By specifying optional argument -e (--check-align), you can make AMAS check if your input files contain only aligned sequences. This option is disabled by default because it can substantially increase computation times in files with many taxa. Enabling this option also provides an additional check against misspecified input file format.

AMAS as a Python module

Using AMAS inside your Python pipeline gives you much more flexibility in how the input and output are being processed. All the major functions of the command line interface can recreated using AMAS as a module. Following installation from pip use:

pydoc amas.AMAS

To access detailed documentation for the classes and functions available.

You can import AMAS to your script with:

from amas import AMAS

The class used to manipulate alignments in AMAS is MetaAlignment. This class has to be instantiated with the same, named arguments as on the command line: in_files, data_type, in_format. You also need to supply the number of cores to be used with cores. MetaAlignment holds one or multiple alignments and its in_files option must be a list, even if only one file is being read.

meta_aln = AMAS.MetaAlignment(in_files=["gene1.phy"], data_type="dna",in_format="phylip", cores=1)

Creating MetaAlignment with multiple files is easy:

multi_meta_aln = AMAS.MetaAlignment(in_files=["gene1.phy", "gene1.phy"], data_type="dna", in_format="phylip", cores=2)

Now you can call the various methods on your alignments. .get_summaries() method will compute summaries for your alignments and produce headers for them as atuple with first element being the header and the second element a list of lists with the statistics:

summaries = meta_aln.get_summaries()

The header is different for nucleotide and amino acid data. You may choose to skip it and print only the second element of the tuple, that is a list of summary statistics:

statistics = summaries[1]

.get_parsed_alignments() returns a list of dictionaries where each dictionary is an alignment and where taxa are the keys and sequences are the values. This allows you to, for example, print only taxa names in each alignment or do other manipulation of the sequence data:

# get parsed dictionaties
aln_dicts = multi_meta_aln.get_parsed_alignments()

# print only taxa names in the alignments:
for alignment in aln_dicts:
    for taxon_name in alignment.keys():

Similar to the above example, it is also easy to get translated amino acid alignment as a list of dictionaries (one per input alignment):

# get parsed dictionaties
aln_dicts = multi_meta_aln.get_translated(2, 1) # 2: vertebrate mitochondrial genetic code and 1: reading frame starting at first character

To split alignment use .get_partitioned("your_partitions_file") on a MetaAlignment with a single input file. .get_partitioned() returns a list of dictionaries of dictionaries, with { partition_name : { taxon : sequence } } structure for each partition:

partitions = meta_aln.get_partitioned("partitions.txt")

AMAS uses .get_partitions("your_partitions_file") to parse the partition file:

parsed_parts = meta_aln.get_partitions("partitions.txt")

.get_replicate(no_replicates, no_loci) gives a list of parsed alignments (dictionaries), each a replicate constructed from the specified number of loci:

replicate_sets = multi_meta_aln.get_replicate(2, 2)

To concatenate multiple alignments first parse them with .get_parsed_alignments(), then pass to .get_concatenated(your_parsed_alignments). This will return a tuple where the first element is the { taxon : sequence } dictionary of concatenated alignment and the second element is the partitions dict with { name : range }.

parsed_alns = multi_meta_aln.get_parsed_alignments()
concat_tuple = multi_meta_aln.get_concatenated(parsed_alns)
concatenated_alignments = concat_tuple[0]
concatenated_partitions = concat_tuple[1]

Removing taxa from alignments is very easy:

spp_to_remove = ["taxon1", "taxon2", "taxon3"]
reduced_alns = multi_meta_aln.remove_taxa(spp_to_remove)

To print to file or convert among file formats use one of the .print_format(parsed_alignment) methods called with a parsed dictionary as an argument. These methods include .print_fasta(), .print_nexus(), .print_nexus_int(), print_phylip(), and .print_phylip_int(). They return an apporpriately formatted string.

for alignment in concatenated_alignments:
    nex_int_string = meta_aln.print_nexus_int(alignment)

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