# Filtering multiple taxa with exact substrings

**URL:** https://forum.qiime2.org/t/filtering-multiple-taxa-with-exact-substrings/21443
**Category:** User Support
**Tags:** taxonomy, filter-features
**Created:** [November 23, 2021, 6:41am UTC](https://forum.qiime2.org/t/filtering-multiple-taxa-with-exact-substrings/21443 "2021-11-23T06:41:18Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![colinbrislawn](https://forum.qiime2.org/user_avatar/forum.qiime2.org/colinbrislawn/32/6221_2.png) [@colinbrislawn](https://forum.qiime2.org/u/colinbrislawn)
#### Post date: [November 24, 2021, 4:43pm UTC](https://forum.qiime2.org/t/filtering-multiple-taxa-with-exact-substrings/21443/2 "2021-11-24T16:43:04Z")

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Hello Hui,

Welcome to the forums! :qiime2:

There is a way to filter multiple taxa at the same time, however I think there's a better way to think about taxa that appear in your negative control.

> [@Yangh191](#):
>
> I have about 20 taxa identified in my negative control. ...  
> I want to to remove these exact 20 taxa in my other groups before running diversity tests.

ah... that might cause other problems. 🙀

The Illumina platform suffers from [index-hopping](https://www.illumina.com/content/dam/illumina-marketing/documents/products/whitepapers/index-hopping-white-paper-770-2017-004.pdf) between samples, and the most abundant amplicons are the most likely to 'hop' into other samples because of a mismatched barcode. This means that a perfectly empty negative control would still get some reads assigned to it by the Illumina sequencer, and essentially be a tiny subset of all real amplicons. **Because this happens during sequencing, real amplicons may end up in empty negative controls.**

> [@Yangh191](#):
>
> In addition, I am looking to removing these taxa proportionally, using modules such as FEAST or SourceTracker2.

That's a much better idea! We have [discussed some methods like this](https://forum.qiime2.org/t/discussion-methods-for-removing-contaminants-and-cross-talk/5626), and I think that's the way to go.

It looks like FEAST it still [tagged as a beta](https://github.com/nchitale/q2-feast), but you could still try and get support from the developer! You could also check out [q2-quality-control](https://docs.qiime2.org/2021.8/tutorials/quality-control/) or [decontam](https://benjjneb.github.io/decontam/vignettes/decontam_intro.html), which have similar goals.

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