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What is Short Read Connector (SRC)?

Short read connector enables the comparisons of two read sets B and Q. For each read from Q it provides either:

  • short_read_connector_counter: The number of occurrences of each k-mers of the read in the set B, or
  • short_read_connector_linker: A list of reads from B that share enough k-mers with the (a window of) the tested read from A.

short_read_connector_counter and short_read_connector_linker both output a text file, as described in the corresponding sections.

These text files can be downstream exploited as described section "Back to reads"

Citation

Marchet, Camille, et al. "A resource-frugal probabilistic dictionary and applications in bioinformatics." Discrete Applied Mathematics 274 (2020): 92-102.

Getting the latest source code

Requirements

Instructions

# get a local copy of source code
git clone --recursive https://github.com/GATB/rconnector.git

# compile the code an run a simple test on your computer
cd rconnector
sh INSTALL

Getting a binary stable release

Binary release for Linux and Mac OSX are provided within the "Releases" tab on Github/rconnector web page.

#short_read_connector_counter

short_read_connector_counter: quick start

Run a simple test counting for each reads from data/c2.fasta.gz, the number of occurrences of each of its kmers (k=31 by default) in data/c1.fasta.gz. Kmers indexed from data/c1.fasta.gz are those occurring at least 2 times (by default).

# First index the kmers from data/c1.fasta.gz:
sh ../short_read_connector_counter.sh index -b data/c1.fasta.gz -i my_counter_index.dumped

# Once indexation is made once, multiple queries may be performed as: 
ls data/c2.fasta.gz > fof.txt # creates a file of files, check the section "Input read sets" for details
sh ../short_read_connector_counter.sh query -i my_counter_index.dumped -q fof.txt  

# Cat short_read_connector_res.txt to check the results

short_read_connector_counter: options

Indexation options

Usage: sh short_read_connector_counter.sh index -b read_file -i dumped_index_name [OPTIONS]
   -b read_files for bank
     Example: -b data/c1.fasta.gz
   -i <string>. File of the index file to be created. Example "my_index.dumped"
   -k <int> value (<32). Set the length of used kmers. Must fit the compiled value. Default=31
   -f <int> value. Fingerprint size. Size of the key associated to each indexed value, limiting false positives. Default=12
   -G <int> value. gamma value. MPHF expert users parameter - Default=2
   -a <int> kmer_abundance_min (kmer from bank seen less than this value both in the bank are not indexed). Default=2
   -l Keep low complexity regions (default false)
   -t <int> number of thread used. Default=0 (all)

Query options

Usage: sh short_read_connector_counter.sh query -i indexed_file -q read_file_of_files [OPTIONS]
MANDATORY:
 -i index created by short_read_connector_counter.sh index (read only)
   Example: -i my_index.dumped
 -q read_file_of_files for query
   Example: -q data/fof.txt (with fof being a file of file descriptor)
OPTIONS:
   -w <int> window_size. See option -s. If the windows size is zero (default value), then the full read is considered. Default=0
   -s <int> kmer_threshold: Minimal percentage of shared kmer span for considering a query read as similar to a data set.  
            The kmer span is the number of bases from the read query covered by a kmer shared with the bank.
   -l Keep low complexity regions (default false)
            If a read of length 80 has a kmer-span of 60, then the percentage of shared kmer span is 75%. If a least a windows (of size "windows_size") contains at least kmer_threshold percent of positions covered by shared kmers, the read is output.
   -p <string> prefix. All out files will start with this prefix. Default="short_read_connector_res"
   -t <int> number of thread used. Default=0 (all)

short_read_connector_counter: output

Two first lines of the output file:

 #query_read_id (from bank data/c2.fasta.gz) mean median min max percentage_shared_positions -- number of shared 31mers with banq my_counter_index.dumped
0 3.614286 4 2 5 100.000000

The first line is the file header. The second line can be decomposed as:

  • 0: id of the query read (from read set contained in fof.txt)

  • 3.614286: mean number of occurrences of its k-mers (here with k=31) in the read set data/c1.fasta.gz

  • 4: median number of occurrences of its k-mers (here with k=31) in the read set data/c1.fasta.gz

  • 2: minimal number of occurrences of at least a kmer from read 0 in the read set data/c1.fasta.gz

  • 5: maximal number of occurrences of at least a kmer from read 0 in the read set data/c1fasta.gz

  • 100.0000: percentage of positions in the best window from the query read (here '0') covered by a kmer indexed in the bank.

Note: it is possible that percentage_shared_positions is equal to 100% while min is equal to 0. This means for instance that at a position i, the kmer starting at this position is not shared but i is covered by a kmer starting at another position.

#short_read_connector_linker

short_read_connector_linker: quick start

Run a simple test counting for each reads from data/c2.fasta.gz, the number of occurrences of each of its kmers (k=31 by default) in data/c1.fasta.gz. Kmers indexed from data/c1.fasta.gz are those occurring at least 2 times (by default).

# First index the kmers from data/c1.fasta.gz:
sh ../short_read_connector_linker.sh index -b data/c1.fasta.gz -i my_linker_index.dumped

# Once indexation is made once, multiple queries may be performed as: 
ls data/c2.fasta.gz > fof.txt # creates a file of files, check the section "Input read sets" for details
sh ../short_read_connector_linker.sh query -i my_linker_index.dumped -q fof.txt  

# Cat short_read_connector_res.txt to check the results

short_read_connector_linker: options

Indexation options

Usage: sh short_read_connector_linker.sh index -b read_file  -i dumped_index_name [OPTIONS]
   -b read_files for bank
     Example: -b data/c1.fasta.gz
   -i <string>. File of the index file to be created. Example "my_index.dumped"
   -k <int> value (<32). Set the length of used kmers. Must fit the compiled value. Default=31
   -f <int> value. Fingerprint size. Size of the key associated to each indexed value, limiting false positives. Default=12
   -G <int> value. gamma value. MPHF expert users parameter - Default=2
   -a <int> kmer_abundance_min (kmer from bank seen less than this value both in the bank are not indexed). Default=2
   -l Keep low complexity regions (default false)
   -t <int> number of thread used. Default=0 (all)

Query options

Usage: sh short_read_connector_linker.sh query -i indexed_file -q read_file_of_files [OPTIONS]
MANDATORY:
 -i index created by short_read_connector_linker.sh index (read only)
   Example: -i my_index.dumped
 -q read_file_of_files for query
   Example: -q data/fof.txt (with fof being a file of file descriptor)
OPTIONS:
   -w <int> window_size. See option -s. If the windows size is zero (default value), then the full read is considered. Default=0
   -s <int> kmer_threshold: Minimal percentage of shared kmer span for considering 2 reads as similar.  
            The kmer span is the number of bases from the read query covered by a kmer shared with the target read.
            If a read of length 80 has a kmer-span of 60 with another read (of unkonwn size) from the bank, then the percentage of shared kmer span is 75%. If a least a windows (of size "windows_size") contains at least kmer_threshold percent of position covered by shared kmers, the read couple is output.
                 TRICK: with kmer_threshold<=0 a single kmer is sufficient in the linker mode to link two reads. 
   -l Keep low complexity regions (default false)
   -p <string> prefix. All out files will start with this prefix. Default="short_read_connector_res"
   -t <int> number of thread used. Default=0 (all)
   -r do not output precision about pair of similar reads. Only ids of reads from queries similar to at least one read from bank are output.

short_read_connector_linker: output

Four first lines of the output file:

#query_read_id [target_read_id-kmer_span (k=31)-kmer_span query_percentage]* or U (unvalid read, containing not only ACGT characters or low complexity read)
#Target read set: my_linker_index.dumped
#Query read set number data/c2.fasta.gz
0:675-93-93.000000 808-89-89.000000

The three first lines are the file header. The last line can be decomposed as:

  • 0: id of the query read

  • 675-93-93.000000: a target read and its peaces of information:

    • 675: id of the targeted read

    • 93: kmer-span (number of position of read 0 that is covered by at least a solid kmer present in read 675)

    • 93.000000: kmer-span ratio wrt to read 0 length (here 100) or to the window size (see option -w)

  • 808-89-89.000000: a second targeted read and its pieces of information (and so on).

Input read sets

We use file of files format for query. The input read sets are provided using a file of file(s). The file of file(s) contains on each line a read file or another file of file(s). Let's look to a few usual cases (italic strings indicate the composition of a file):

  • Case1: I've a unique read set composed of a unique read file (reads.fq.gz). fof.txt containsreads.fq.gz

  • Case2: I've a unique read set composed of a couple of read files (reads_R1.fq.gz andreads_R2.fq.gz). This may be the case in case of pair end sequencing. fof.txt containsfof_reads.txt:

 with fof_reads.txt:

 * reads_R1.fq.gz
 * reads_R2.fq.gz
  • Case3: I've two read sets each composed of a unique read file: reads1.fq.gz and reads2.fq.gz:
fof.txt:
reads1.fq.gz
reads2.fq.gz
  • Case4: I've two read sets each composed two read files: reads1_R1.fq.gz and reads1_R2.fq.gz and reads2_R1.fq.gzandreads2_R2.fq.gz:
fof.txt:
fof_reads1.txt
fof_reads2.txt

withfof_reads1.txt:

reads1_R1.fq.gz
reads1_R2.fq.gz

with fof_reads2.txt:

reads1_R1.fq.gz
reads1_R2.fq.gz

and so on...

 

Back to reads

Using the short read connector output, it is possible to select reads from the query file that meets user defined requirements. It is done using two executables: generate_bv and extract_reads_from_bv.

  • generate_bv extract query reads whose similarity with the bank is higher than a user defined threshold. Its takes as input a short read connector output (counter or linker), a percentage threshold and it generates a boolean vector (.bv file) containing a readable comment and a compressed 0/1 vector. 0 designs reads the do not meet the similarity threshold and vice versa.

    • With short read connector linker it contains all reads from a query bank that are similar (depending on -s and -w options) to at least a read from the bank

    • With short read connector counter it contains all reads from a query bank that are similar (depending on -s and -w options) to the bank

  • extract_reads_from_bv takes as input a read set and a related .bv file and outputs the reads corresponding to ones in the .bv file.

 

Contact

Contact: Pierre Peterlongo: pierre.peterlongo@inria.fr