A bacteria that can create calories out of thin air sounds like it’d be useful, if true.
The belief in bacteria causing obesity is so prevalent in the medical world, that you can’t donate fecal matter for a fecal transplant if you’re above a certain body fat percentage, because it’s believed bacteria obese people carry that caused them to become obese will make a thin person obese if the bacteria is transplanted to the thin person from the obese person.
A healthy gut microbiome may help regulate the calories extracted from food, but no bacteria will create calories out of nothing.