We can live without bateria if we add with some food supplements.
mitochondria isn't considered alive, as a separate organism, AFAIK. It doesn't even have a species name. It's just a component of the host cell.
As I understand it, these new microorganisms are parasites. They're not essential for the functioning of the host cell like mitochondria are.
Citation needed. I would strongly doubt that this is true, because microbes also play a very important role in eg. immune defense. Remove all the mutualitic microbes from a human (eg skin, digestive tract) and the parasitic and pathogenic bacteria will take their place immediately.
There are sterile mice made for scientific uses - 100% mouse, completely microorganism free or your money back. They have health issues, but they can survive and reproduce in the right conditions.
Of course, those "right conditions" include sterile housings and sterilized food, because they'll get contaminated otherwise.
That is interesting! Is it because they are missing functions which bacteria offers?
Ship of Theseus, obviously.