Hi @vkk_24!
Not one that we release on the QIIME 2 website, but others must be out there, since there have been a few forum users who report using nifH in QIIME 2.
I recommend contacting the makers of that database to ask them if they have any ideas, they would have the best advice on how to convert to fasta and extract taxonomy information. They might even be interested in making a Q2 compatible release...
Here is another forum topic that is pretty similar to yours and answers at least the second of these questions (and requires starting with fasta). It sounds like @EGvibrio was using a custom database — nevertheless, perhaps @EGvibrio has some advice or has worked with the jzehr nifH database? :
I have not worked with nifH personally, but know of some nifH mock communities on mockrobiota, where the contributor recommended another nifH database released by jzehr, so maybe this would be something useful?: https://wwwzehr.pmc.ucsc.edu/CART_model_public/
Let's see if @EGvibrio or others who have worked with nifH might have any advice!