Whilst the L. reuteri are oddly fermenting (I'm not quite sure, it smells and tastes somewhat like tangy cheese), I've found a connection between GABA and the microbiome.
Essentially, not only does the notorious gut-brain-axis rely much on a GABA-producing microbiome raising GABA in serum and brain!
But a lot of bacteria of a (healthy?) microbiome exclusively depend on GABA as a crucial nutrient.
Many bacteria don't grow at all without exogenous GABA, which should be supplied by other bacteria of the microbiome.
Hence, supplementing GABA feeds such bacteria and reconstitutes gastrointestinal microbiotic diversity.
And feeding GABA increases IFN-y for innate immunity, TNF-a, MUC2 for the crucial mucin barrier.
Also, feeding GABA appears to enhance autophagy of enteric cells instead of them taking the route of destructive apoptosis.
GABA-producing gut bacteria are foremost Bacteroides (e.g. fragilis), Parabacteroides, Eschericia, L. plantarum, L. brevis, L. lactis, L. paracasei.
GABA content in fermented dairy (cheese) varies a lot depending on the microbiotic strains being traditionally used in the respective regions (huge differences e.g. just among the Italian Pecorino cheeses).
GABA-modulating bacteria of the human gut microbiota
I'm now supplementing c. 3grs GABA every day.
Have already felt the "heavy chest" and mild flushing for a couple of hours after my intake, as reported by others in the RPF.