blast_best_hit: Retrieve only the best BLAST hit for each query

In drostlab/metablastr: Perform Massive Local BLAST Searches

Retrieve only the best BLAST hit for each query

Description

This function performs a BLAST search between query and subject sequences and returns only the best hit based on the following criteria.

A best blast hit is defined as:

• the hit with the smallest e-value

• if e-values are identical then the hit with the longest alignment length is chosen

Usage

blast_best_hit(
  query,
  subject,
  search_type = "nucleotide_to_nucleotide",
  strand = "both",
  output.path = NULL,
  is.subject.db = FALSE,
  task = "blastn",
  db.import = FALSE,
  postgres.user = NULL,
  evalue = 0.001,
  out.format = "csv",
  cores = 1,
  max.target.seqs = 10000,
  db.soft.mask = FALSE,
  db.hard.mask = FALSE,
  blast.path = NULL
)

Arguments

query	path to input file in fasta format.
subject	path to subject file in fasta format or blast-able database.
search_type	type of query and subject sequences that will be compared via BLAST search. Options are: search_type = "nucleotide_to_nucleotide" search_type = "nucleotide_to_protein" search_type = "protein_to_nucleotide" search_type = "protein_to_protein"
strand	Query DNA strand(s) to search against database/subject. Options are: strand = "both" (Default): query against both DNA strands. strand = "minus" : query against minus DNA strand. strand = "plus" : query against plus DNA strand.
output.path	path to folder at which BLAST output table shall be stored. Default is output.path = NULL (hence getwd() is used).
is.subject.db	logical specifying whether or not the subject file is a file in fasta format (is.subject.db = FALSE; default) or a blast-able database that was formatted with makeblastdb (is.subject.db = TRUE).
task	BLAST search task option (depending on the selected search_type). Options are: search_type = "nucleotide_to_nucleotide" task = "blastn" : Standard nucleotide-nucleotide comparisons (default) - Traditional BLASTN requiring an exact match of 11. task = "blastn-short" : Optimized nucleotide-nucleotide comparisons for query sequences shorter than 50 nucleotides. task = "dc-megablast" : Discontiguous megablast used to find somewhat distant sequences. task = "megablast" : Traditional megablast used to find very similar (e.g., intraspecies or closely related species) sequences. task = "rmblastn" search_type = "nucleotide_to_protein" task = "blastx" : Standard nucleotide-protein comparisons (default). task = "blastx-fast" : Optimized nucleotide-protein comparisons. search_type = "protein_to_nucleotide" task = "tblastn" : Standard protein-nucleotide comparisons (default). task = "tblastn-fast" : Optimized protein-nucleotide comparisons. search_type = "protein_to_protein" task = "blastp" : Standard protein-protein comparisons (default). task = "blast-fast" : Improved BLAST searches using longer words for protein seeding. task = "blastp-short" : Optimized protein-protein comparisons for query sequences shorter than 30 residues.
db.import	shall the BLAST output be stored in a PostgresSQL database and shall a connection be established to this database? Default is db.import = FALSE. In case users wish to to only generate a BLAST output file without importing it to the current R session they can specify db.import = NULL.
postgres.user	when db.import = TRUE and out.format = "postgres" is selected, the BLAST output is imported and stored in a PostgresSQL database. In that case, users need to have PostgresSQL installed and initialized on their system. Please consult the Installation Vignette for details.
evalue	Expectation value (E) threshold for saving hits (default: evalue = 0.001).
out.format	a character string specifying the format of the file in which the BLAST results shall be stored. Available options are: out.format = "pair" : Pairwise out.format = "qa.ident" : Query-anchored showing identities out.format = "qa.nonident" : Query-anchored no identities out.format = "fq.ident" : Flat query-anchored showing identities out.format = "fq.nonident" : Flat query-anchored no identities out.format = "xml" : XML out.format = "tab" : Tabular separated file out.format = "tab.comment" : Tabular separated file with comment lines out.format = "ASN.1.text" : Seqalign (Text ASN.1) out.format = "ASN.1.binary" : Seqalign (Binary ASN.1) out.format = "csv" : Comma-separated values out.format = "ASN.1" : BLAST archive (ASN.1) out.format = "json.seq.aln" : Seqalign (JSON) out.format = "json.blast.multi" : Multiple-file BLAST JSON out.format = "xml2.blast.multi" : Multiple-file BLAST XML2 out.format = "json.blast.single" : Single-file BLAST JSON out.format = "xml2.blast.single" : Single-file BLAST XML2 out.format = "SAM" : Sequence Alignment/Map (SAM) out.format = "report" : Organism Report
cores	number of cores for parallel BLAST searches.
max.target.seqs	maximum number of aligned sequences that shall be retained. Please be aware that max.target.seqs selects best hits based on the database entry and not by the best e-value. See details here: https://academic.oup.com/bioinformatics/advance-article/doi/10.1093/bioinformatics/bty833/5106166 .
db.soft.mask	shall low complexity regions be soft masked? Default is db.soft.mask = FALSE.
db.hard.mask	shall low complexity regions be hard masked? Default is db.hard.mask = FALSE.
blast.path	path to BLAST executables.

Author(s)

Hajk-Georg Drost

See Also

blast_nucleotide_to_nucleotide, blast_protein_to_protein, blast_nucleotide_to_protein, blast_protein_to_nucleotide, blast_best_reciprocal_hit

Examples

## Not run: 
blast_best_test <- blast_best_hit(
                 query   = system.file('seqs/qry_nn.fa', package = 'metablastr'),
                 subject = system.file('seqs/sbj_nn_best_hit.fa', package = 'metablastr'),
                 search_type = "nucleotide_to_nucleotide",
                 output.path = tempdir(),
                 db.import  = FALSE)
                 
 # look at results
 blast_best_test

## End(Not run)

drostlab/metablastr documentation built on Sept. 14, 2023, 10:43 a.m.