how to set database other than nr for remote blast+ search
I believe you're looking for env_nr? It's listed as such, under Metagenomic proteins in the blastp webpage. It appears that the word within brackets should be supplied alongside the -db parameter. A quick test with a dummy amino acid fasta file does turn up a result to a valid NCBI protein accession.



Edit: I followed up on this with a little more digging around, and it appears the database you're looking for is called Microbial_proteins. I ended up quote-searching Microbial proteins from nr on Google and exactly 2 hits turn up. The first hit, I think, is what the OP posted a screenshot of in a comment to this answer. The second is a list of databases along with keywords from a Spain-based bioinformatics firm: http://data.biobam.com/ncbi_blast_dbs_protein.pdf. I retried the dummy example with the Microbial_proteins database, and it seems to work. Again, I am not sure why I can't easily find this on an NCBI resource. Also, I am curious as to how different this database is from env_nr.