See also
FASTQ files
Quality scores
FASTQ format options
The fastq_join command combines paired reads into single sequences by reverse-complementing the reverse read and inserting padding (default NNNNNNNN). If R1 is the forward read and R2 is the reversed read, the combined read is R1 NNNNNNNN RevComp(R2).
The forward (R1) read filename is given by the fastq_join option.
The reverse (R2) read filename is given by the -reverse option.
The -join_padgap option specifies the letters to use for padding, default NNNNNNNN.
The -join_padgapq option specifies the Q score ASCII characters to use for padding, default IIIIIIII (8 x Q=40 with ASCII_BASE 33).
The output is written to a FASTQ file by specifying the -fastqout option and/or to a FASTA file given by -fastaout.
Example
usearch -fastq_join fwd.fastq -reverse rev.fastq -fastaout join.fa