Custom Database Kraken2 with Metagenomes

Question

[alenew.am]

Hi guys, i have to create a custom database for kraken2 and i have multiple directories, each containing a metagenome (composed by contigs), so in total i have multiple multi-fastas. How can i do? have i to write in each sequence of each metagenome the name of the organism/taxa id and then create a single multi-fasta file with all the sequences together?

Thanks

[GenoMax]

It is not clear where the information about the ID/name is going to come from. Do you want to overwrite the header that is already there or add to it?

Here are some examples of past threads that may be useful: How To Rename FASTA Headers and Renaming fasta headers according to a matching name list

[alenew.am]

Thanks for your reply! At the moment the name of each directory containing the reads and all the headers of the reads are alphanumeric codes. But i also have an excel file that match every directory name with a classification label (from kingdom to species if available). I think that kraken uses the information in the sequence header to assign the classification label and so my doubt about the renaming/adding of this information in the header.