In the Titan habitability calculation, we estimated the total amount of cell mass that could be supported by glycine fermentation based on the estimate glycine delivery from the top surface all the way through 100 km of ice into the deep subsurface ocean of Titan.
And we came up with a small dog's worth of cell mass.
Affholder et al. 2025 (open-access article): https://iopscience.iop.org/article/10.3847/PSJ/adbc66