In BONCAT or Substrate Analog Probing (SAP), a modified version of an amino acid or substrate is incubated with the sample, which is followed by a click-chemistry reaction to add a fluorescent probe \cite{Hatzenpichler_2015a}.
The combination of amplicon sequencing with SIP has enabled the detection of not only rarer organisms but even low enrichment levels through statistical modelling \cite{Barnett2019}.
Nucleic acids targeted in SIP can be separated from the unlabelled ones using a bouyant density gradient (for DNA or RNA). 
Due to these database challenges, ASVs within a given soil study are most likely similar to a given taxon at the phylum level but cannot be described at lower taxonomic ranks.
It can even occur that different species can have an identical 16S rRNA gene or IT sequence, making species delineation nearly impossible with the amplicon sequencing approach. The assumed conservation of function applied in such software packages faces the same challenges.