Hello everyone, I'm seeking clarification on the relationship between OTU, ASV, and Kraken2, which confuses me.

I understand that with the OTU approach, sequences are grouped into clusters if they have a similarity above a pre-set threshold, and these sequences are then compared to a database. On the other hand, the ASV approach does not involve clustering and uses a denoising approach.

However, I'm confused about the position of Kraken2. It is a taxonomic classification system that uses exact k-mer matches. Does this mean that it uses a different system from OTU or ASV, or does it use one of these systems and then move on to exact k-mer matches?

Any clarification would be helpful because I'm finding it difficult to understand. Thank you in advance.