As of release 138 the SILVA databases, its taxonomy, and all files provided for
download are licensed unter Creative Commons Attribution 4.0 (CC-BY 4.0).

All data is freely available for academic and commercial use as long as SILVA
is credited as original author and a link to the full license is provided.

The full license is available:
    https://creativecommons.org/licenses/by/4.0/ and
    https://creativecommons.org/licenses/by/4.0/legalcode