It ranks only second to cellulose as the single most important organic molecule on Earth. The exoskeleton of many invertebrates such as shrimp and crabs is composed of chitin. Life on Earth depends on the degradation of insoluble, polymeric, organic molecules such as chitin to its inorganic constituents such as carbon dioxide and nitrate, which are essential nutrients for photosynthetic plants such as algae and diatoms.
Marine microorganisms are the primary degraders of chitin in the ocean.
Degradation involves the breaking of chemical bonds between sugar residues that comprise the chitin molecule. Enzymes known as chitinases are responsible for the initial steps in the degradation process. The chitinase enzymes are excreted by bacteria that have become attached to the exoskeleton after the animal has died. In order for these enzymes to gain access to the insoluble chitin molecules, they must be positioned outside the bacterial cell but maintained close to the cell surface so that the bacteria has access to the sugar subunits which it can transport into the cell and metabolize. The sugars derived from chitin are used by the bacterial cells to produce more chitinase enzymes and new bacterial cells.