Dr Jay Davidson gives you basic knowledge about those gut bugs, healthy bacteria or as it's called mitochondria.  "Mitochondria are well-known as the powerhouses of the cell and are found within almost all living cells in varying numbers. They are small organelles floating freely through the cell that act like a digestive system, taking in nutrients, breaking them down, and creating energy-rich molecules (ATP) for the cell. These processes of the cell are known as cellular respiration. [1]"