small size, just about every piece of “food” for bacteria is relatively large. In order for bacteria to get the nutrition they need, the molecules must be small enough to pass through the bacteria’s cell membrane. Therefore, they have the following options if they want to “eat.”
Use the small molecules that already exist in their surrounding environment.
Rely on natural processes to create new small molecules in their surrounding environment.
Develop a way to break down large molecules into more manageable smaller molecules they can use.
Since small molecules are not always readily available (1) and relying on natural processes to break large molecules down into smaller ones can be SLOW (2) bacteria need a mechanism they can rely on to actively create molecules small enough that they can absorb into their cells (3).
Without hands, teeth, or physical tools, bacteria use enzymes to chemically break down larger organic molecules into smaller ones that can pass through their cell membranes. These enzymes are produced inside the bacteria, and are released through their membrane to act along the surface of and on the outside of their cells. Bacteria and other microbes (phytoplankton) in the ocean are constantly creating and using ectoenzymes (enzymes that function on or outside the cell) to “cut” large molecules of organic matter in the water to smaller more usable molecules.