Wild organism thriving but gravity stable

I captured some wild organisms and inoculated wort with them, as described in this post:

https://www.homebrewtalk.com/f163/isolated-wild-something-id-help-wanted-243306/

It went from malt agar to Sabouraud agar to hopped wort and grew in each medium.

After a few weeks, the organism in question has thrived, produced some pleasant aromas, and is forming a cake on the bottom. The strange thing is that the gravity hasn't appreciably changed from the SG (1.060), which puzzles me. Any idea what sort of bug could do that? If it hasn't been consuming sugars all this time, what exactly has it been using?

I guess I'm in the market for a microscope now because I'm dying to figure out what the heck this thing is even if I can't use it.

A common thread between the different types of media that the organism has been able to grow on is protein. I'd bet that it is using amino acids not only as a carbon source, but also as an energy source. (Some amino acids can be converted to oxaloacetate or pyruvate.)

Posting photos of the colonies would be helpful, as would identifying the antibiotic that you used in the Sabouraud agar when culturing this thing.