Where biofilms are found

Biofilms may form:
1.  on solid substratums in contact with moisture,
2.  on soft tissue surfaces in living organisms, and 
3.  at liquid-air interfaces. 

Typical locations for biofilm production include rock and other substratum surfaces in marine or freshwater environments.

This pristine lake is in the northern Rocky Mountains of Montana. Biofilm communities formed in this environment may be composed of a range of different types of organisms, both autotrophic and heterotrophic.

©Gordon McFeters, author. ASM MicrobeLibrary

Biofilms form in the summer on surfaces within pristine aquatic systems such as the one shown here in the northern Rocky Mountains in Montana.

Algae derive their energy from photosynthesis and their carbon from dissolved carbon dioxide. Bacteria, which are generally heterotrophic, obtain their energy from organic matter produced by the algae or from organic matter washing into the lake from the surrounding terrestrial habitat.

Biofilms are an important life link in many natural communities. These organisms form the basis for food webs that nourish larger organisms such as insect larvae which are consumed by fish that are in turn consumed by birds like eagles. This biofilm came from a pristine aquatic alpine ecosystem, and is viewed through a conventional microscope.

©Gordon McFeters, author. ASM MicrobeLibrary
Biofilm from an aquatic alpine ecosystem.

The larger, roughly spherical cells that  appear green to brown are algae while the smaller dark cells are associated bacteria.  Both types of cells produce  a polymeric extracellular slime layer which encloses the  cells. This complex aggregate of cells and  polysaccharide  is the biofilm community.

Microbial mats are specialized microbial communities composed mainly of photosynthetic procaryotes. The principle distinction between microbial mats and other biofilms is their dependence on photosynthesis as their primary source of energy.

A microbial mat. Photo by John Lennox

This microbial mat was found in a roadside puddle in Pennsylvania. The mat formed quickly in summer weather and demonstrates that it is not necessary to travel to exotic locations in order to study complex and interesting biofilm communities.

Biofilms are also commonly associated with living organisms, both plant and animal. Tissue surfaces such as teeth and intestinal mucosa which are constantly bathed in a rich aqueous medium, rapidly develop a complex aggregation of microorganisms enveloped in an extracellular polysaccharide matrix. The ASM biofilm image collection contains many such images in its medical slide set.

One image from the ASM collection (shown here), is a scanning electron micrograph (SEM) of the mucous layer of the small intestine of a mouse. The image illustrates how organisms live within the mucous  layer and on the villi. Note the way the mucous layer covers the villi and the relative depth of the layer.

© W. Costerton, K. Lam, K. Rozee, authors. ASM MicrobeLibrary
Organisms living on the mucous layer of a mouse's small intestine.

Here, human dental plaque has been exposed to 5% sucrose  for 5 minutes before applying Gram's iodine (0.33% Iodine  in 0.66% KI).

©J.D. Ruby, V.F. Gerencser, authors.ASM MicrobeLibrary
Dental plaque stained with Gram's iodine.

The sucrose solution was applied to the left central incisor (which appears on the right) while the right central incisor served as a control.  Iodine selectively binds to alpha-1,4 glucans (iodophilic polysaccharide, i.e.  glycogen or amylose), resulting in  brown to purple staining.

The ability of oral bacteria to store iodophilic polysaccharides or glycogen-like molecules inside their cells is associated with dental caries since these storage compounds may extend the time during which lactic acid formation may occur. It is this prolonged exposure to lactic acid which results in decalcification of tooth enamel. 

Plants commonly have microbial populations associated  with their external tissues.  One beneficial type of plant-microbe relationship occurs in the rhizosphere between the plant roots, root hairs and a complex microbial community. 

© G.  Trolldenier, author. ASM MicrobeLibrary
Roots of Red Clover with adhering bacteria.

Plant roots secrete significant amounts of sugars, amino acids, vitamins and plant hormones which stimulates microbial growth in the  root.  This microbial growth may facilitate the plant's ability to absorb nutrients from the soil.  In this way,  it becomes a mutualistic and beneficial relationship to the plant and the microbes.

Introduction
Where biofilms are found
How biofilms form
Biofilm attributes
Facts about biofilms
A misconception

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Supported in part by the Waksman Foundation for Microbiology
Developed in collaboration with Dr. John Lennox, Education Editor, Penn State Altoona
©2002-2006 Center for Biofilm Engineering, http://www.erc.montana.edu

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