The gut, or gastrointestinal tract (GI tract) is where is all happens. It is where you digest your food and where you get all your energy. It is the one function of the body that if it goes wrong, your whole body will feel the effects in short order.
The GI tract is comprised of an array of organs that process your food and protect the body from the other items such as bad bacteria and viruses that make it into your food and water throughout the day. But the bulk of the genes in the gut are bacterial based such that the gut flora (or beneficial bacteria) is commonly referred to as the “forgotten organ” since it plays such a vital role in your digestive tract.
And different bacterial species live in different regions of the gut. Some like high acid regions of the stomach and some like low acid regions of the small intestine. Just like you have organs that secrete different enzymes in the mouth, stomach, and small intestine, you have different enzymes coming from the bacteria that also provide essential roles indigestion in the various GI regions. Much of this information is now being discovered.