Combine collapsed read files into a single DB

Given a set of FASTA Ribo-Seq read files that have been collapsed from FASTQ format to take the following format:

>seq<read_number>_x<read count>
NNNNNNNNNNNNNNNNNNNNNNNNNNNNN

Example:

>seq1_x15121
ACGTACGCAGTTTTATCCGGTAAAGCGAATGA

combine these read files so the sequence is stored just once and the counts are recorded per sample