relationship between relative abundance and relative activity

Question

[bitpir]

Hello, I have a bunch of meta-transcriptomics data and I would like to identify which organism is the most active. I plan to calculate TPM/RPKM for each organism and the figure out the "most-active" organism that way. However, I find that this method is over-simplified as I am not taking into account the relative abundance (genome copy number) into my calculation, right? If so, what's the best way to calculate relative activity from meta-trancriptomic data then?

Thank you so much for your help!

[ATpoint]

First you should clearly define/explain what "most active" is. Is this referring to a specific gene? Or rather which organism is most abundant in the metasample?

[bitpir]

I think that is something I am struggling with too. I think what I want to get at is to figure out which organism is transcribing the most, i.e most viable?