I deal with a lot of OTU tables and some of them go down to the species level, some are unknown but go down to the family level, etc. I'll get some statistics with an interesting group but how can I put some biological meaning on these groups of organisms (OTUs annotated by either Silva, RDP, or Green Genes)?

How can I say microbial group A is enriched in these types of organisms when compared to microbial group B? Types being defined as known to be associated with a certain function (e.g. nitrogren fixation, biofilm production, virulent, etc).