By entering one or more taxonomy identifiers (taxid), the search will be restricted to only those sequences in the database belonging to these organisms. The resulting e-values will be given as if the database only consisted of these sequences. If left empty your search will not be restricted by organisms, but will run as normal. Taxid example: "9606" restricts to human sequences. A comma separated list like: "9606,10090" restricts to human and mouse sequences.