I'm not an expert, just someone who is interested in gut microbiome. I doubt that you would get accurate results if you used a single species or even a blend of species. Prescript Assist contains the widest range of probiotics I've seen (think it was 42 strains) but it will not begin to compare with what really goes on in the gut. A really healthy person may have as many as 7000 species.

I did come across somewhere in Australia that was trying to make an artificial gut. Think it was Prof Thomas Borody. He was doing this to create replacement material for faecal transplants.

You may find a faecal sample will give you a good starting point.

I agree. It is not hard to get a fecal transplant from a bank for research purposes. This would be pre-screened for health of donor.

Shah P, Fritz JV, Glaab E, Desai MS, Greenhalgh K, Frachet A, Niegowska M, Estes M, Jäger C, Seguin-Devaux C, Zenhausern F, Wilmes P. A microfluidics-based in vitro model of the gastrointestinal human-microbe interface. Nat Commun. 2016 May 11;7:11535. doi: 10.1038/ncomms11535.

An Artificial Gut for Microbiome Studies 05/30/2016 Kristie Nybo, PhD

https://www.biotechniques.com/news/An-Artificial-Gut-for-Microbiome-Studies/biotechniques-364528.html

Have you ever heard the organ-on- a- chip? I am not sure in which state they are but they were also trying intestine on a chip to figure out how a microbiome shift effects the other organs. I don't know rest of the team (5 Dutch university with many researchers). But one of the PI from Groningen University was Cisca Wijmenga. I don't know your final aim but it might be useful. And I am agreed on the researchers previous comments. The gut-microbiome diversity is way big to be tested invitro. And also from the comparison of the feces metagenomes you may hardly get a match to carry out (cheap way) invitro.

Thank you Orchan for your suggestion.