Bacterial mat

Note 1: A biofilm is a system that can be adapted internally to environmental conditions by its inhabitants.

A biofilm is any group of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances (EPS). The EPS components are produced by the cells within the biofilm and are typically a polymeric conglomeration of extracellular DNA, proteins, and polysaccharides. Because they have three-dimensional structure and represent a community lifestyle for microorganisms, biofilms are frequently described metaphorically as "cities for microbes."

Biofilms may form on living or non-living surfaces and can be prevalent in natural, industrial and hospital settings. The microbial cells growing in a biofilm are physiologically distinct from planktonic cells of the same organism, which, by contrast, are single-cells that may float or swim in a liquid medium. Biofilms can be present on the teeth of most animals as dental plaque, where they may cause tooth decay and gum disease.

Microbes form a biofilm in response to many factors, which may include cellular recognition of specific or non-specific attachment sites on a surface, nutritional cues, or in some cases, by exposure of planktonic cells to sub-inhibitory concentrations of antibiotics. When a cell switches to the biofilm mode of growth, it undergoes a phenotypic shift in behavior in which large suites of genes are differentially regulated. According to the textbook entitled "Microbiology an Introduction" states In nature, microorganisms seldom live in the isolated single-species colonies that we see on laboratory plates. The live in communities called biofilms. A biofilm may also be considered a hydrogel, which is complex polymer containing many times it's dry weight in water. Biofilms are not just bacterial slime layers but biological systems; the bacteria are organized into a coordinated functional community. Biofilms can be attached to a surface such as a tooth, rock, or surface which may include a single species or of a diverse group of microorganisms. The biofilm bacteria are able to share nutrients and are shltered from harmful factors in the environment, such as desiccation, antibiotics, and the body's immune system. A biofilm usually begins to form when a free-swimming bacterium attaches to a surface.

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