Gut Flora Bleg

     Almost sounds German.  Do any of you know much about gut flora?  I know it refers to the trillions of bacteria, along with fungi and protozoa, that live inside every person's gastro-intestinal tract.  I understand most of it is just 30-40 types in each person, but how many, of the hundreds or even thousand of different types might be one of the 30-40 types that are most numerous?  Is there a list of their secretions somewhere?  Do we know what types of things (things that might normally happen inside a gi-tract) can kill each type?  Do we know the effects if, say, your ABC bacteria group is actually sub-type 3a of ABC which often succumbs when the person has a high fever, and it all dies?