I think there's a more than fair chance that B vitamin deficiencies are at the heart of most PD. Whether that is problem is created via bacteria imbalances in the colon, or the blood brain barrier mechanism probably varies. It wouldn't surprise me if the research in intestinal biotics unearths a bunch of new treatments for a wide scale of illnesses. It's really a new frontier in medicine.

Keep in mind though that too much Prevotellaceae is commonly found in arthritis patients, so careful what you wish for.

When it comes to fecal transplants there is much to be learned. I had an exchange once with a researcher on this and he said that when they transplanted from anxious mice to calm mice, those mice became anxious as well. The brain/small intestine connection is very poorly understood at the moment.