HOWTO:BlastPlus

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Abstract

Using BioPerl to create, manage, and query BLAST databases using the NCBI's blast+ suite.

Quicklink to Synopsis.

Contents


Author

Mark A. Jensen

Fortinbras Research

maj -at- fortinbras -dot- us

Introduction

blast+ is a suite of programs from the NCBI that create, manipulate, manage and query BLAST sequence databases. The Bio::Tools::Run::StandAloneBlastPlus package attempts to integrate the many blast+ programs into a wrapper providing a unified programmatic interface to these programs, with BioPerl objects as input and output if desired.

Dependencies and Installation

Bio::Tools::Run::StandAloneBlastPlus (r16783) and Bio::Tools::Run::StandAloneBlastPlus::BlastMethods (r16834) can be found in the master of bioperl-run. These depend on a lower-level wrapper, Bio::Tools::Run::BlastPlus and Bio::Tools::Run::BlastPlus::Config (@ r16472 in bioperl-run), and extensions to Bio::Tools::Run::WrapperBase, Bio::Tools::Run::WrapperBase::CommandExts (@ r16780), in the master of bioperl-live.

To download and install BioPerl core and packages from github see Using Git.

Like all run wrappers, these modules need the underlying programs to work. Get blast+ 2.2.22 at the NCBI FTP site: [1]. The user manual is very helpful.

Overview

The Bio::Tools::Run::StandAloneBlastPlus object is a "factory" or harness that directs the execution of the various blast+ programs. The basic mantra is to (1) create a StandAloneBlastPlus factory using the new() constructor, and (2) perform BLAST analyses by calling the desired BLAST program by name off the factory object. The database can be pre-existing, or can be created directly using a FASTA file or a BioPerl sequence collection object. Low-complexity or other masking can also be applied as the database is constructed.

The BLAST database itself and any masking data are attached to the factory object (step 1). Query sequences and any parameters associated with particular programs are provided to the blast method call (step 2), and are run against the attached database. (We present step 2 first, since it's what people will do many times after creating their database once.)

blast+ also provides facilities for blasting sequences against NCBI databases over the network. See Remote BLAST for details.

BLAST method execution

Given a StandAloneBlastPlus factory, such as

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
   -db_name => 'testdb'
);

(see factory construction below) you can run the desired BLAST method directly from the factory object, against the database currently attached to the factory (in the above example, testdb). -query is a required argument:

$result = $fac->blastn( -query => 'query_seqs.fas' );

Here, $result is a Bio::Search::Result::BlastResult object. To obtain further results, use next_result:

while ($result = $fac->next_result) {
 ...
}

Rewind to the beginning of the results:

$fac->rewind_results;
while ($result = $fac->next_result) {
 ...
}

BLAST methods include blastn, blastp, blastx, tblastn, tblastx, rpsblast, psiblast, rpstblastn, as well as others I probably forget. For more details on parsing and processing the results, see the SearchIO HOWTO.


Note the following details:

  • The blast output file can be named explicitly:
$result = $fac->blastn( -query => 'query_seqs.fas',
                        -outfile => 'query.bls' );
  • The output format can be specified:
$result = $fac->blastn( -query => 'query_seqs.fas',
                        -outfile => 'query.bls',
                        -outformat => 5 ); # 5=XML output
  • Additional arguments to the method can be specified:
$result = $fac->blastn( -query => 'query_seqs.fas',
                        -outfile => 'query.bls',
                        -method_args => [ '-num_alignments' => 10 ,
                                          '-evalue' => 100 ]);
  • To get the name of the blast output file, do
$file = $fac->blast_out;
  • To clean up the temp files (you must do this explicitly):
$fac->cleanup;

Running bl2seq

Running bl2seq is similar to running the methods as outlined above, but both -query and -subject parameters are required required, and the attached database is ignored. The BLAST method must be specified explicitly with the -method parameter:

$fac->bl2seq( -method => 'blastp',
              -query => $seq_object_1,
              -subject => $seq_object_2 );

Other parameters ( -method_args, -outfile, and -outformat ) are valid.

Return values

The return value is always a Bio::Search::Result::BlastResult object on success, undef on failure.

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Database construction

Factory construction and initialization

First of all, the factory needs to be told where the blast+ programs live. The BLASTPLUSDIR environment variable will be checked for the default executable directory. Alternatively, the program directory can be set for individual factory instances using the -prog_dir constructor parameter. All the blast+ programs must be accessible from that directory (i.e., as executable files or symlinks).

Either the database or BLAST subject data must be specified at factory construction. Databases can be pre-existing formatted BLAST dbs, or can be built directly from fasta sequence files or BioPerl sequence object collections of several kinds. The key constructor parameters are -db_name, -db_data, and -db_dir.

To specify a pre-existing BLAST database, use -db_name alone:

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
      -db_name => 'mydb'
);

The directory can be specified along with the basename, or separately with -db_dir:

 
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
     -db_name => '~/home/blast/mydb'
);
 
#same as
 
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
    -db_name => 'mydb', -db_dir => '~/home/blast'
);

To create a BLAST database de novo, see Creating a BLAST database.

If you wish to apply pre-existing mask data (i.e., the final ASN1 output from one of the blast+ masker programs), to the database before querying, specify it with -mask_file:

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
    -db_name => 'mydb', -mask_file => 'mymaskdata.asn'
);

Creating a BLAST database

There are several options for creating the database de novo using attached data, both before and after factory construction. If a temporary database (one that can be deleted by the cleanup() method) is desired, leave out the -db_name parameter. If -db_name is specified, the database will be preserved with the basename specified.

Use -create => 1 to create a new database (otherwise the factory will look for an existing database). Use -overwrite => 1 to create and overwrite an existing database.

Note that the database is not created immediately on factory construction. It will be created if necessary on the first use of a factory BLAST method, or you can force database creation by executing

$fac->make_db();

Specify data during construction

With a FASTA file:

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'mydb',
  -db_data => 'myseqs.fas',
  -create => 1
);

With another BioPerl object collection:

$alnio = Bio::AlignIO->new( -file => 'alignment.msf' );
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'mydb',
  -db_data => $alnio,
  -create => 1
);
@seqs = $alnio->next_aln->each_seq;
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'mydb',
  -db_data => \@seqs,
  -create => 1
);

Other collections (e.g., Bio::SeqIO) are valid. If a certain type does not work, please submit an enhancement request.

To create temporary databases, leave out the -db_name, e.g.

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_data => 'myseqs.fas',
  -create => 1
);

To get the tempfile basename, do:

$dbname = $fac->db;

Specify data post-construction

After the factory has been created, you can use the explict attribute setters:

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -create => 1
);
 
$fac->set_db_data('myseqs.fas');
$fac->make_db;

and so on.

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Creating and using mask data

The blast+ mask utilities windowmasker, segmasker, and dustmasker are available. Masking can be rolled into database creation, or can be executed later. If your mask data is already created and in ASN1 format, set the -mask_file attribute on construction (see Factory construction/initialization).

To create a mask from raw data or an existing database and apply the mask upon database creation, construct the factory like so:

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'my_masked_db',
  -db_data => 'myseqs.fas',
  -masker => 'dustmasker',
  -mask_data => 'maskseqs.fas',
  -create => 1
);

The masked database will be created during make_db().

The -mask_data parameter can be a FASTA filename or any BioPerl sequence object collection. If the datatype (nucl or prot) of the mask data is not compatible with the selected masker, an exception will be thrown with a message to that effect.

To create a mask ASN1 file that can be used in the -mask_file parameter separately from the attached database, use the make_mask() method directly:

$mask_file = $fac->make_mask(-data => 'maskseqs.fas',
                             -masker => 'dustmasker');
# segmasker can use a blastdb as input
$mask_file = $fac->make_mask(-mask_db => 'mydb',
                             -masker => 'segmasker')
 
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'my_masked_db',
  -db_data => 'myseqs.fas',
  -mask_file => $mask_file
  -create => 1
);

Getting database information

To get a hash containing useful metadata on an existing database (obtained by running blastdbcmd -info), use db_info():

# get info on the attached database..
$info = $fac->db_info;
# get info on another database
$info = $fac->db_info('~/home/blastdbs/another');

To get a particular info element for the attached database, just call the element name off the factory:

$num_seqs = $fac->db_num_sequences;
# info on all the masks applied to the db, if any:
@masking_info = @{ $fac->db_filter_algorithms };

Accessing the Bio::Tools::Run::BlastPlus factory

The blast+ programs are actually executed by a Bio::Tools::Run::BlastPlus wrapper instance. This instance is available for peeking and poking in the StandAloneBlastPlus factory() attribute. For convenience, BlastPlus methods can be run directly from the StandAloneBlastPlus object, and are delegated to the factory() attribute.

For example, to get the blast+ program to be executed, examine either

$fac->factory->command

or

$fac->command

Similarly, the currently set parameters for the BlastPlus factory are

@parameters = $fac->get_parameters

To get a list of what parameters you can set for the current blast+ operation, do:

@available = $fac->available_parameters('all');

Cleaning up temp files

Temporary analysis files produced under a single factory instances can be unlinked by running

$fac->cleanup;

Tempfiles are generally not removed unless this method is explicitly called. Note that cleanup() only unlinks "registered" files and databases. All temporary files are automatically registered; in particular, "anonymous" databases (such as

$fac->Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_data => 'myseqs.fas', 
  -create => 1
);

without a -db_name specification) are registered for cleanup. Any file or database can be registered with an internal method:

$fac->_register_temp_for_cleanup('testdb');

Remote BLAST

StandAloneBlastPlus can access NCBI databases remotely. Just create a factory with the desired database and -remote => 1:

$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'nr',
  -remote => 1
);

and call BLAST methods from the factory as usual. Note that the database info methods are unavailable for remote databases. Available remote databases are listed here.

Other database goodies

  • You can check whether a given basename points to a properly formatted BLAST database by doing
$is_good = $fac->check_db('putative_db');
  • User parameters can be passed to the underlying blast+ programs (if you know what you're doing) with db_make_args and mask_make_args:
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'customdb',
  -db_data => 'myseqs.fas', 
  -db_make_args => [ '-taxid_map' => 'seq_to_taxa.txt' ],
  -masker => 'windowmasker',
  -mask_data => 'myseqs.fas',
  -mask_make_args => [ '-dust' => 'T' ],
  -create => 1
);
  • You can prevent exceptions from being thrown by failed blast+ program executions by setting no_throw_on_crash(). Examine the error with stderr():
$fac->no_throw_on_crash(1);
$fac->make_db;
if ($fac->stderr =~ /Error:/) {
   #handle error
   ...
}
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Synopsis

# existing blastdb:
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'mydb'
);
 
# create blastdb from fasta file and attach
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'mydb',
  -db_data => 'myseqs.fas',
  -create => 1
);
 
# create blastdb from BioPerl sequence collection objects
$alnio = Bio::AlignIO->new( -file => 'alignment.msf' );
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'mydb',
  -db_data => $alnio,
  -create => 1
);
 
# blast against the remote NCBI db
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'nr',
  -remote => 1
);
 
@seqs = $alnio->next_aln->each_seq;
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
  -db_name => 'mydb',
  -db_data => \@seqs,
  -create => 1
);
 
# create database with masks
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
 -db_name => 'my_masked_db',
 -db_data => 'myseqs.fas',
 -masker => 'dustmasker',
 -mask_data => 'maskseqs.fas',
 -create => 1
);
 
# create a mask datafile separately
$mask_file = $fac->make_mask(
  -data => 'maskseqs.fas',
  -masker => 'dustmasker'
);
 
# query database for metadata
$info_hash = $fac->db_info;
$num_seq = $fac->db_num_sequences;
@mask_metadata = @{ $fac->db_filter_algorithms };
 
# perform blast methods
$result = $fac->tblastn( -query => $seqio );
 
# create a factory:
$fac = Bio::Tools::Run::StandAloneBlastPlus->new(
   -db_name => 'testdb'
);
 
# get your results
$result = $fac->blastn( -query => 'query_seqs.fas',
                        -outfile => 'query.bls',
                        -method_args => [ '-num_alignments' => 10 ] );
 
$result = $fac->tblastx( -query => $an_alignment_object,
                         -outfile => 'query.bls',
                         -outformat => 7 );
 
# do a bl2seq
$fac->bl2seq( -method => 'blastp',
              -query => $seq_object_1,
              -subject => $seq_object_2 );
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