Running locally blastn against nt db thru python script - python-2.7

Question

I have a fasta file with sequence that I want to blast locally to 'nt' database dowloaded on my computer from ncbi website
I dowloaded blast 2.6.0.
In order to access blast from anywhere, I did:
gedit ~/.bashrc
export PATH=/usr/local/ncbi-blast-2.6.0+/bin:$PATH
then I did:
source ~/.bashrc
Then I downloaded 'nt' database (155.6GB) and stored it in /usr/local/blastdb
I want to run in python script this command:
from Bio.Blast.Applications import NcbiblastnCommandline
cline = NcbiblastnCommandline(query="/home/proprietaire/Desktop/JADE/stage_scripts/seq_error_fasta.fasta", db="/usr/local/blastdb/nt", evalue=0.001, out="blast_result_local.xml", outfmt=5)
But it is not working for a reason. Please help me figure out what I'm doing wrong. Thank you for your help.
EDIT:
'seq_error_fasta.fasta' : is my fasta file with 64 sequences that I want to blast to 'nt' database.
My 'seq_error_fasta.fasta' contains sequence loaded with error like S, J, X so I want to blast them to 'nt' db in order to get the closest better sequence
I found out that I need to format the nt database dowloaded from ncbi so I did this:
makeblastdb -dbtype nucl -in nt
Then I added this after my cline variable in my python script:
stdout, stderr = cline()
The script is running but unfortunately I'm getting this error now:
Bus error (core dumped)
I think it's a ram memory problem so I thought that I need to shorten 'nt' db by taking only the bacteria sequence. I looked on NCBI for a whole bacteria only database but there is multiple database of different species like more then a thousand.
I also tried blast online using this script:
f = open('output_blast.xml','w')
for rec in SeqIO.parse(open("seq_error_fasta.fasta"), 'fasta):
result_handle = NCBIWWW.qblast("blastn", "nt", rec.format("fasta"), format_type="XML", alignments=1, perc_ident=95, expect= 0.001)
f.write(result_handle.read())
f.close()
but this only doing one query sequence and returning all hits, althought I specified 1 hit and 95% of identity.
This is driving me crazy lollll Please help

Answer 1

Download NCBI nr database:
$ mkdir db
$ cd db
$ wget ftp://ftp.ncbi.nlm.nih.gov/blast/db/nr*
Run blast:
import io
import shlex
import subprocess
BLAST_OUTFMT6 = """\
'6 qacc sacc pident length mismatch gapopen qstart qend sstart send evalue bitscore qseq sseq'\
"""
BLAST_OUTFMT6_COLUMN_NAMES = [
'query_id', 'subject_id', 'pc_identity', 'alignment_length', 'mismatches', 'gap_opens',
'q_start', 'q_end', 's_start', 's_end', 'evalue', 'bitscore', 'qseq', 'sseq',
]
def blastp(sequence, db, evalue=0.001, max_target_seqs=100000):
system_command = (
'blastp -db {db} -outfmt {outfmt} -evalue {evalue} -max_target_seqs {max_target_seqs}'
.format(db=db, outfmt=BLAST_OUTFMT6, evalue=evalue, max_target_seqs=max_target_seqs)
)
cp = subprocess.Popen(
shlex.split(system_command),
stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
universal_newlines=True)
result, error_message = cp.communicate(sequence)
if error_message.strip():
print("Error: {}".format(error_message))
return result
if __name__ == '__main__':
result = blastp('AAAAAAAAAAAAAA', db='/path/to/db/nr')
print(result)