OTU QC: PhiX spike-in
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11-Aug-2018 New paper describes octave plots for visualizing alpha diversity.

12-Jun-2018 New paper shows that one in five taxonomy annotations in SILVA and Greengenes are wrong.

18-Apr-2018 New paper shows that taxonomy prediction accuracy is <50% for V4 sequences.

05-Oct-2017 PeerJ paper shows low accuracy of closed- and open-ref. QIIME OTUs.

22-Sep-2017 New paper shows 97% threshold is wrong, OTUs should be 99% full-length 16S, 100% for V4.

UPARSE tutorial video posted on YouTube. Make OTUs from MiSeq reads.



OTU QC: PhiX spike-in

See also
  Quality control for OTU sequences

A PhiX spike-in is used for Illumina sequencing of amplicon libraries for 16S and other marker genes. Then, PhiX is typically found in around 5% of the raw reads. Often, these are filtered before you see the FASTQ files, but not always, and third-party PhiX filtering software may not be accurate. In usearch, PhiX search is based on the ublast algorithm, and is very sensitive.

The search_phix command can be used for searching and the filter_phix command can be used for filtering.