make.contigs gets short reads

Hi All,

I am following Miseq SOP to treat V3-V4 2*300 raw data with the initial make.contigs(ffastq=f1.fastq,rfastq=r1.fastq) command. But I get some short reads with only ~50 bp .I am wondering this normal for the V3-V4 data, or I made some mistakes in the command.

Thanks

mothur >
make.contigs(ffastq=17.fastq,rfastq=17-1.fastq,processors=4)

Using 4 processors.
Making contigs…
Done.
It took 34 secs to process 72348 sequences.


Output File Names: 17.trim.contigs.fasta 17.scrap.contigs.fasta 17.trim.contigs.qual 17.scrap.contigs.qual 17.contigs.report

[WARNING]: your sequence names contained ‘:’. I changed them to ‘_’ to avoid problems in your downstream analysis.

mothur >
summary.seqs(fasta=17.trim.contigs.fasta)

Using 4 processors.

Start End NBases Ambigs Polymer NumSeqs
Minimum: 1 35 35 0 2 1
2.5%-tile: 1 39 39 0 3 1809
25%-tile: 1 42 42 0 4 18088
Median: 1 58 58 0 5 36175
75%-tile: 1 465 465 0 6 54262
97.5%-tile: 1 465 465 3 13 70540
Maximum: 1 601 601 252 188 72348
Mean: 1 240.971 240.971 0.500387 5.38984

of Seqs: 72348

Output File Names:
17.trim.contigs.summary

It took 1 secs to summarize 72348 sequences.

That is weird. Have you looked at any of the short sequences to see what they are? FWIW, you might be interested in this post

Pat