Biofilms are the result of adhesion and growth of microorganisms at interfaces. They consist mainly of water (70-95 % wet weight), held by the highly hydrated extracellular polymers (EPS, 70-95 % dry weight) in which the microorganisms are embedded. Adhering cells differ from their suspended counterparts in both activity and resistance to toxic substances. The cells are immobilized next to each other and form well organized consortia, capable of performing sequential degradation processes. Biofilms are ubiquitous and the majority of microorganisms on earth is living in biofilms. The particular properties of biofilms are utilized for environmental protection in bioreactor technology, applied to sewage water and waste air purification, soil remediation and solid waste decomposition. Biofilms can have detrimental effects, inducing metal corrosion and microbially induced weathering of mineral materials such as stone or cement. Resulting damage, e.g., to oil tanks and pipelines and to concrete sewers, has lead to substantial pollution of soil, groundwater and surface water. Biofilm development on heat exchangers, filter materials and separation membranes leads to the application of large amounts of biocides. These cause waste water problems after use. A deeper understanding of the particular properties and dynamics of biofilm development and processes could help to optimize the application of desired biofilms and to minimize the detrimental effects of undesired biofilms and of countermeasures.
