Our reference database pre-processing pipeline is based on in silico amplification to extract only the region of interest. However, it appears that most of the priming region for the primer 27F (which is used with the 338R primer to cover the regions V1V2) is not included into the full-length 16S rRNA reference database of EzBioCloud. Thus, this pre-processing won't work with this pre-processing pipeline and this database.
valscherz
commented
3 years ago 
Our reference database pre-processing pipeline is based on in silico amplification to extract only the region of interest. However, it appears that most of the priming region for the primer 27F (which is used with the 338R primer to cover the regions V1V2) is not included into the full-length 16S rRNA reference database of EzBioCloud. Thus, this pre-processing won't work with this pre-processing pipeline and this database.
27F: 5′-AGMGTTYGATYMTGGCTCAG-3′
338R: 5′-GCTGCCTCCCGTAGGAGT-3′