I’ve been following the Moving Pictures tutorial generally for both an ITS and 16s libraries (Miseq multiplexed 300bp single-end) with a Keemei-checked mapping file with the correct barcodes. We’ve successfully used a different pipeline earlier for these specific libraries - so we know generally what the data should look like (and that the data is good).
However, in our Qiime2 results for both libraries, most of the sequences appear to be in only one sample - with a few sequences appearing exactly once in a few samples. Based on our older analysis, there are 96 samples total that should have a relatively even spread of reads from 100's of OTUs.
We didn’t trim primers/adapters since the Miseq data doesn’t include them in the sequences. (Although I saw a post where someone's Miseq data where their Illumina did have both forward and reverse primers included?)
I'm wondering if I'm misunderstanding a step, or there are actually primers/adapters in our sequences that are causing the DADA2 to put almost all sequences in one sample? Thank you in advance for any insights!
Here are the Qiime2 commands I used:
qiime tools import
--type MultiplexedSingleEndBarcodeInSequence
--input-path L1P1.fastq.gz
--output-path multiplexed-seqs.qza
--i-seqs multiplexed-seqs.qza
--m-barcodes-file map_k.tsv
--m-barcodes-column BarcodeSequence
--p-error-rate 0
--o-per-sample-sequences demultiplexed-seqs.qza
--o-untrimmed-sequences untrimmed.qza
--verbose
--i-data demultiplexed-seqs.qza
--o-visualization demultiplexed-seqs.qzv
#The quality was good enough for all of the lengths, so I set the trunc length to the maximum it would #allow: 298bp.
--i-demultiplexed-seqs demultiplexed-seqs.qza
--p-trim-left 0
--p-trunc-len 298
--o-representative-sequences rep-seqs-dada2.qza
--o-table table-dada2.qza
--o-denoising-stats stats-dada2.qza
qiime feature-table tabulate-seqs
--i-data rep-seqs-dada2.qza
--o-visualization rep-seqs.qzv
qiime tools export
--input-path table-dada2.qza
--output-path exported-feature-table
#Visualize table file as a .tsv file. This will give OTU ID, Sample ID, and counts in a table.
qiime feature-table summarize
--i-table table-dada2.qza
--o-visualization table.qzv
--m-sample-metadata-file map.tsv