 Unlike most organisms, they are able to use their own enzymes to digest plant biopolymers such as cellulose or lignin.Collagen, an abundant structural protein in animals, and keratin—a protein that forms hair and nails—, can also serve as food sources.Unusual examples include "Aureobasidium pullulans", which feeds on wall paint, and the kerosene fungus "Amorphotheca resinae", which feeds on aircraft fuel (causing occasional problems for the airline industry), and may sometimes block fuel pipes.