You can't find a single case study where someone's consciousness was notably altered due to bowel resection. Something that has happened all the time.
Where are the people losing or having alerted consciousness after having their stomachs stapled? Their perforated bowels resected? Their bowel cancer polyps removed?
The closest you'll find is soldiers suffering from, understandable, PTSD.
Also, I'd point out that the studies you referenced aren't suggesting your point. They are saying that the gut can affect our mood and cravings. But as anyone that's taken a powerful antibiotic can attest, that did not modify their consciousness even though it nuked a huge portion of their biome.
People also get fecal transplants, they don't share consciousness as a result.
Unless you want to define consciousness as an eternal soul that exists in rocks, then you'll find no support for the suggestion that it exists outside a brain.
You also need to explain why it is that traumatic brain injuries alter consciousness and memory. Why it is that we can observe physical changes in the brains of dementia patients.
Let's wait and see what happens with brain or head transplantation. :)