A colony of bacteria and other microorganisms that adheres to a substrate and is enclosed and protected by secreted slime. Biofilms readily form on virtually any surface, whether nonliving or living, where there is moisture and a supply of nutrients. They are important components of aquatic and terrestrial ecosystems, typically providing nutrients for small organisms at the base of food chains. Moreover, they form in the microenvironment (rhizosphere) surrounding plant roots, where they assist the plant in absorbing nutrients from the soil. Cells in such colonies secrete chemical signals that recruit neighbouring cells and also produce a matrix of polysaccharides and proteins that binds the colony members together and to the substrate. Channels through the colony allow cells in the interior access to nutrients, and information about the size of the colony is transmitted by a mechanism called quorum sensing. Biofilms can also occur in the body and in industrial installations. For example, dental plaque is a bacterial biofilm that forms on the surface of teeth and causes tooth decay, and biofilms on hospital equipment are often resistant to eradication and a persistent source of infection. In industry biofilms are common in water-based processes and can clog up and corrode pipelines, but can also be beneficial, as demonstrated by their role in sewage treatment.