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Abstract

Biofilms and microbial mats can be defined as surface-associated layers of microbial
cells embedded in extracellular polymeric substance (EPS; Characklis and Marshall,
1989; Stal and Caumette, 1994). Biofilms cover solid surfaces, while mats cover
sediments. Biofilms range from a few cell layers to a maximum of a few mmillimeters
in thickness, and microbial mats range from <1 mm to several centimeters in thick-
ness. Furthermore, most microbial mats are characterized by high population densi-
ties of photoautotrophic microorganisms that act as primary producers in the top
millimeters and build up the mat matrix, while many biofilms are heterotrophic and
rely on substrate supply from the surface or the surrounding water. Despite these
fundamental differences, biofilms and microbial mats share many characteristics, and
both represent communities with complex strategies for microbial life at surfaces where
steep gradients of physicochemical variables are found (chapters 8 and 14).