Grep that tolerates mismatches to subset .fastq

问题

I am working with bash on a linux cluster. I am trying to extract reads from a .fastq file if they contain a match to a queried sequence. Below is an example .fastq file containing three reads.

$ cat example.fastq

@SRR1111111.1 1/1
CTGGANAAGTGAAATAATATAAATTTTTCCACTATTGAATAAAAGCAACTTAAATTTTCTAAGTCG
+
AAAAA#EEEEEEEEEEEEEEEEEEEEEEEAEEEEEEEEEEEEEEEEEEEEEEEEEA<AAEEEEE<6
@SRR1111111.2 2/1
CTATANTATTCTATATTTATTCTAGATAAAAGCATTCTATATTTAGCATATGTCTAGCAAAAAAAA
+
AAAAA#EE6EEEEEEEEEEEEAAEEAEEEEEEEEEEEE/EAE/EAE/EA/EAEAAAE//EEAEAA6
@SRR1111111.3 3/1
CTATANTATTGAAATAATAATGTAGATAAAACTATTGAATAACAGCAACTTAAATTTTCAATAAGA
+
AAAAA#EE6EEEEEEEEEEEEAAEEAEEEEEEEEEEEE/EAE/EAE/EA/EAEAAAE//EEAEAA6

I would like to extract reads containing the sequence GAAATAATA. I can perform this extraction using grep as shown in the following command.

$ grep -F -B 1 -A 2 "GAAATAATA" example.fastq > MATCH.fastq

$ cat MATCH.fastq

@SRR1111111.1 1/1
CTGGANAAGTGAAATAATATAAATTTTTCCACTATTGAATAAAAGCAACTTAAATTTTCTAAGTCG
+
AAAAA#EEEEEEEEEEEEEEEEEEEEEEEAEEEEEEEEEEEEEEEEEEEEEEEEEA<AAEEEEE<6
@SRR1111111.3 3/1
CTATANTATTGAAATAATAATGTAGATAAAACTATTGAATAACAGCAACTTAAATTTTCAATAAGA
+
AAAAA#EE6EEEEEEEEEEEEAAEEAEEEEEEEEEEEE/EAE/EAE/EA/EAEAAAE//EEAEAA6

However, this strategy does not tolerate any mismatches. For example, a read containing the sequence GAAATGATA will be ignored. I need this extraction to tolerate one mismatch at any position in the queried sequence. So my question is how can I achieve this? Is there a sequence alignment package available with similar functionality to grep? Are there any fastq subsetting packages available that perform this type of operation? One note is that speed is very important. Thanks for your guidance.

回答1:

Here is a solution using agrep to get the record numbers of matches and an awk that prints out those records with some context (due to missing -Aand -B in agrep):

$ agrep -1 -n  "GAAATGATA" file | 
  awk -F: 'NR==FNR{for(i=($1-1);i<=($1+2);i++)a[i];next}FNR in a' - file

Output:

@SRR1111111.1 1/1
CTGGANAAGTGAAATAATATAAATTTTTCCACTATTGAATAAAAGCAACTTAAATTTTCTAAGTCG
+
AAAAA#EEEEEEEEEEEEEEEEEEEEEEEAEEEEEEEEEEEEEEEEEEEEEEEEEA<AAEEEEE<6
@SRR1111111.3 3/1
CTATANTATTGAAATAATAATGTAGATAAAACTATTGAATAACAGCAACTTAAATTTTCAATAAGA
+
AAAAA#EE6EEEEEEEEEEEEAAEEAEEEEEEEEEEEE/EAE/EAE/EA/EAEAAAE//EEAEAA6

回答2:

You might try a file of patterns -

$: cat GAAATAATA
.AAATAATA
G.AATAATA
GA.ATAATA
GAA.TAATA
GAAA.AATA
GAAAT.ATA
GAAATA.TA
GAAATAA.A
GAAATAAT.

then

grep -B 1 -A 2 -f GAAATAATA example.fastq > MATCH.fastq

but it will probably slow the process down a bit to add both full regex parsing AND an alternate pattern for each possible single change...

responding to question in comments:

For a given value of $word, such as word=GAAATAATA,

awk '{
  for ( i=1; i<=length($0); i++ ) {
     split($0,tmp,""); tmp[i]=".";
     for ( n=1; n<=length($0); n++ ) { printf tmp[n]; }
     printf "\n";
  }
}' <<< "$word" > "$word"

This will create this specific file. Hope that helps, but remember that this will be a lot slower since you are now using regexes instead of just matching plain strings, AND you are introducing a whole series of alternate patterns to match...

回答3:

This should work but idk if the MATCH.fastq in your question is the expected output or not or even if your sample input contains any cases that need a working solution to find so idk if it's actually working or not:

$ cat tst.awk
BEGIN {
    for (i=1; i<=length(seq); i++) {
        regexp = regexp sep substr(seq,1,i-1) "." substr(seq,i+1)
        sep = "|"
    }
}
{ rec = rec $0 ORS }
!(NR % 4) {
    if (rec ~ regexp) {
        printf "%s", rec
    }
    rec = ""
}

$ awk -v seq='GAAATAATA' -f tst.awk example.fastq
@SRR1111111.1 1/1
CTGGANAAGTGAAATAATATAAATTTTTCCACTATTGAATAAAAGCAACTTAAATTTTCTAAGTCG
+
AAAAA#EEEEEEEEEEEEEEEEEEEEEEEAEEEEEEEEEEEEEEEEEEEEEEEEEA<AAEEEEE<6
@SRR1111111.3 3/1
CTATANTATTGAAATAATAATGTAGATAAAACTATTGAATAACAGCAACTTAAATTTTCAATAAGA
+
AAAAA#EE6EEEEEEEEEEEEAAEEAEEEEEEEEEEEE/EAE/EAE/EA/EAEAAAE//EEAEAA6

来源：https://stackoverflow.com/questions/53768447/grep-that-tolerates-mismatches-to-subset-fastq

标签

awk

grep

bioinformatics

fastq

sequencing