# Basic questions regarding classic OTU table in QIIME2

**URL:** https://forum.qiime2.org/t/basic-questions-regarding-classic-otu-table-in-qiime2/4189
**Category:** User Support
**Tags:** pending-development
**Created:** [May 17, 2018, 3:55pm UTC](https://forum.qiime2.org/t/basic-questions-regarding-classic-otu-table-in-qiime2/4189 "2018-05-17T15:55:32Z")
**Posts on this page:** 1
**Showing post:** 6

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### Author: ![FranciscoC](https://forum.qiime2.org/user_avatar/forum.qiime2.org/franciscoc/32/5210_2.png) [@FranciscoC](https://forum.qiime2.org/u/FranciscoC)
#### Post date: [May 18, 2018, 4:07pm UTC](https://forum.qiime2.org/t/basic-questions-regarding-classic-otu-table-in-qiime2/4189/6 "2018-05-18T16:07:15Z")

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Dear Nicholas,

Thank you very much for the answers. After your explanation its pretty clear the advantage of a unique OTU ID instead of an arbitrary number.

Regarding the Biom convertion, I was following the "Moving Pictures" tutorial and have combined the sequence variant ID with the taxonomy, following a post of the forum ([How to make classic otu table with QIIME2?](https://forum.qiime2.org/t/how-to-make-classic-otu-table-with-qiime2/3612)). I got stuck on the final step when converting the biom format to txt.

The code is the following:

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qiime tools export table.qza --output-dir exported  
qiime tools export taxonomy.qza --output-dir exported

#####Change the first line of biom-taxonomy.tsv (i.e. the header) to this:

#OTUID  
#taxonomy  
#confidence

biom add-metadata -i exported/feature-table.biom -o table-with-taxonomy.biom --observation-metadata-fp exported/biom-taxonomy.tsv --sc-separated taxonomy

#convert to classic table

biom convert -i table-with-taxonomy.biom -o OTU\_Table.txt --to-tsv --header-key taxonomy

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