Chitin
Chitin is a polymer, a repeating arrangement of a chemical structure. Chitin is found in the supporting structures of many organisms. Of relevance to microbiology, chitin is present in fungal species such as mushrooms, where it can comprise from 5% to 20% of the weight of the organism.
The backbone of chitin is a six-member carbon ring that has side groups attached to some of the carbon atoms. This structure is very similar to that of cellulose. One of the side groups of chitin is known as acetamide, whereas cellulose has hydroxy (OH) side groups.
Chitin is a noteworthy biological feature because it is constructed solely from materials that are naturally available. In contrast, most polymers are man-made and are comprised of constituents that must be artificially manufactured.
The purpose of chitin is to provide support for the organism. The degree of support depends on the amount and the thickness of chitin that is present. In fungi such as mushrooms, chitin confers stability and rigidity, yet allows some flexibility. This allows the mushrooms to stand and still be flexible enough to sway without snapping.
The role of chitin as a support structure is analogous to the peptidoglycan supportive layer that is a feature of Gram-positive and Gram-negative bacteria. The think peptidoglycan layer in Gram-positive bacteria provides a rigid and robust support. The peptidoglycan layer in Gram-negative bacteria that is only one molecule thick does not provide the same degree of structural support. Other mechanical elements of the Gram-negative cell wall are necessary to shore up the structure.
In the ocean, where many creatures contain chitin, sea-dwelling bacteria called Vibrio furnisii have evolved a sensory system that detects discarded chitin. The bacteria are able to break down the polymer and use the sugar molecules as metabolic fuel.
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