I'm sorry if this is a repeated question, but I continue to have doubts.

I created a blastdb like this: 

    makeblastdb -in input.fasta -dbtype nucl -title test_DB -parse_seqids -out test_DB

But I can't understand how to add the taxid in order to have the same result has if I used the all nt database.

Can someone clarify me? Thanks
your command should look like:

    makeblastdb -in input.fasta -dbtype nucl -title test_DB -parse_seqids -taxid_map taxidmapfile -out test_DB 

The taxidmap file is a text file consisting of two columns. 
You can download the taxonomy id information here:

ftp://ftp.ncbi.nih.gov/pub/taxonomy/accession2taxid/nucl_gb.accession2taxid.gz

You need to unpack it and you can make a taxidmap file by doing (something like):

```
sed '1d' nucl_gb.accession2taxid | awk '{print $2" "$3}' > taxidmapfile
```