def MergeReads(R1, R2, outname, read_length):
    usearch = args.usearch
    pretrim_R1 = outname + '.pretrim_R1.fq'
    pretrim_R2 = outname + '.pretrim_R2.fq'
    ufitslib.log.debug("Removing index 3prime bp 'A' from reads")    
    cmd = ['vsearch', '--fastq_filter', R1, '--fastq_trunclen', str(read_length), '--fastqout', pretrim_R1]
    ufitslib.runSubprocess(cmd, ufitslib.log)
    cmd = ['vsearch', '--fastq_filter', R2, '--fastq_trunclen', str(read_length), '--fastqout', pretrim_R2]
    ufitslib.runSubprocess(cmd, ufitslib.log)

    #next run USEARCH mergepe
    merge_out = outname + '.merged.fq'
    skip_for = outname + '.notmerged.R1.fq'
    ufitslib.log.debug("Now merging PE reads")
    cmd = [usearch, '-fastq_mergepairs', for_reads, '-reverse', rev_reads, '-fastqout', merge_out, '-fastqout_notmerged_fwd', skip_for,'-minhsp', '12','-fastq_maxdiffs', '8']
    ufitslib.runSubprocess(cmd, ufitslib.log)

    #now concatenate files for downstream script
    outname = outname + '.fq'
    final_out = os.path.join(args.out, outname)
    with open(final_out, 'w') as cat_file:
        shutil.copyfileobj(open(merge_out,'rU'), cat_file)
        if args.rescue_forward == 'on':
            shutil.copyfileobj(open(skip_for,'rU'), cat_file)
    #count output
    origcount = ufitslib.countfastq(R1)
    finalcount = ufitslib.countfastq(final_out)
    pct_out = finalcount / float(origcount)

    #clean and close up intermediate files
    return'{0:,}'.format(finalcount) + ' reads passed ('+'{0:.1%}'.format(pct_out)+')')
if not args.taxonomy:
    #start with less common uses, i.e. Blast, rdp
    if args.method == 'blast':
        #check if command line blast installed
        if not ufitslib.which('blastn'):
            ufitslib.log.error("BLASTN not found in your PATH, exiting.")
        #now run blast remotely using NCBI nt database
        outformat = "6 qseqid sseqid pident stitle"
        if args.local_blast:
            #get number of cpus
            cpus = multiprocessing.cpu_count() - 2
  "Running local BLAST using db: %s" % args.local_blast)
            cmd = ['blastn', '-num_threads', str(cpus), '-query', args.fasta, '-db', os.path.abspath(args.local_blast), '-max_target_seqs', '1', '-outfmt', outformat, '-out', blast_out]
            ufitslib.runSubprocess(cmd, ufitslib.log)
  "Running BLASTN using NCBI remote nt database, this may take awhile")
            cmd = ['blastn', '-query', args.fasta, '-db', 'nt', '-remote', '-max_target_seqs', '1', '-outfmt', outformat, '-out', blast_out]
            ufitslib.runSubprocess(cmd, ufitslib.log)
        #load results and reformat
        new = []
        f = csv.reader(open(blast_out), delimiter='\t')
        for col in f:
            query = col[0]
            gbID = col[1].split("|")[3]
            pident = col[2]
            name = col[3]
            tax = gbID + ";" + name + " (" + pident + ")"
            line = [query,tax]