ABSTRACT
Micro-organisms, like the vast majority of living creatures, tend to live in communities and form their own specific habitats. It has been estimated that up to 90% of microbial cells in nature grow within agglomerates (Costerton et al., 1987). Microbial films, frequently designated as biofilms, are one of the types of biological agglomerates (together with flocs and granules). They are communities of microorganisms attached to surfaces, forming a porous matrix which contains the cells, the extracellular polymeric substances (EPS) they produce, and a substantial amount of water (Characklis and Marshall, 1990; Melo et al., 1992). In nature and industry, this biofilm concept is
obviously too simple and should be extended to include organic debris and small inorganic particles (clays, metallic oxides, etc.) captured by the polymeric network, as well as adsorbed compounds. Microbial cells in biofilms are often bacteria, but living algae and fungi often appear in significant quantity in such matrices. In some cases, macro-organisms such as mussels and barnacles may attach to the microbial layer. Microorganisms in biofilms can survive in extreme conditions, with pH ranging from 0 to more than 13, temperatures from –10°C to 120°C or higher, and even in ultra-pure water (Flemming, 1991).
