New here. Sorry about having put it in the wrong thread and for not having elaborated how this is testable enough.
How it is testable:
All they'd have to do is run psychological tests on people having them guess what's on each other's minds or for example guess who is more or less likely to come into a room a person is in and tests on their gut bacteria in controlled settings over a period of time and repeat the studies. Perhaps you'd see similar gut bacteria means higher rates of accurate guessing. Or perhaps not. Either way I'd be interested in seeing the results and even wonder if perhaps studies like this have been conducted. If they have then clearly they came out either negative or inconclusive (or else we would've all heard about this), which would still be great to know. If not someone should get to work on that. I'll grant even if the results showed a correlation gut flora influence on personality characteristics would still be a viable explanation so then we'd need to conduct yet more research.
We could have tests on the precise behaviors of these bacterias both with their own species and others and how they react when exposed to various chemicals found in the human body, as well as to test how each set of molecules and chemicals (including the microbes themselves) interact with one another based on what you'd expect to find in the human body as well as the air that people breathe. Run some calculations and they should be able to say whether this is at least a possibility and ultimately yes prove or disprove the theory. If the mathematics of a microbial populations' interactions with themselves and their environment happened to coincide with the way that humans interact (or exhibit even higher levels of complexity) with each other and their environment there would be no reason to say they aren't conscious and indeed intelligent. If the material interactions look exactly the same physically when analyzed from every angle then it is exactly the same and can be characterized as being conscious and possessing humanlike intelligence. Of course if the mathematics were to show they don't line up at all then the theory would be falsified.
Monosigna in particular. There's got to be more information on that other than that their communication patterns are more complex than humans. I'd love to see the full mathematics of it so I could begin parsing out how they interact and whether there are any major parallels with how the matter and energy we call "humans" interacts with each other. But everytime I try looking for more information on that subject I can't find anything. If anybody could direct me towards any relevant information on Monosigna that would be great. It's next to impossible for me to find through regular search engines.
Maybe I'd find something completely different, still worth the search.
Edit:
It's Monosiga Brevicollis not Monosigna. I can't locate the original article that claims their communication is more complex than humans but I did find an article that says their tyrosine kinase signaling network is more complex than any other protist.
http://www.ncbi.nlm.nih.gov/pubmed/18621719
Disregard what I said about it being more complex than humans, granted that would be amazing if it were and it's likely it would require a great deal more tests and analysis (such as what I described could be done above) to figure that out. Or we already know in which case the helpful people here can point me to the specific pieces of information to either confirm or deny and either way it's always good to learn more information.