For the majority of microorganisms the adherence to some kind of surface is essential for optimal living conditions including protection against external influences such as temperature, pH, or even biocidal agents. The resultant surface growth of organisms and their products, the extracellular polymeric substances (EPS), form biofilms, which tend to coat virtually every material surface in contact with water. The attachment of microorganisms to surfaces and the involved EPS play a pivotal role in bio corrosion/ bio deterioration of materials and bioleaching of various minerals (mainly metal sulphide ores) including the formation of acid rock/mine drainage (ARD/AMD).
Both, microbially influenced corrosion (MIC) and bioleaching are processes characterized by dissolution processes of substrata (controlled and uncontrolled). For a better control of both processes, an understanding of the structure and function of EPS of corrosion-causing and leaching microorganisms is of crucial importance.
Bioleaching is applied successfully as a technology for metal recovery worldwide. The predominant bioleaching microorganisms are extremely acidophilic bacteria and archaea (i.e. microorganisms that thrive at pH below 3). They are able to oxidize reduced inorganic sulfur compounds (RISCs) and/or iron(II)-ions. The two well-established bioleaching modes are “non-contact” and “contact” leaching. The latter takes into account that cells attach and form biofilms on the surface of minerals. During bioleaching of ores, a formation of various redox reaction products and mineral phase transformations as well as changes in the microbial community structure takes place. All these modify the interfacial interactions defining the bioleaching behaviour and metal extraction efficiency. In order to characterize such complex interactions, in-situ techniques e.g. synchrotron-radiation techniques and omics methodologies are applied.
MIC refers to the deterioration of materials, such as steel and concrete. Bio corrosion is the result of electro/chemical reactions influenced or driven by microorganisms, which are often present as biofilms. In recent years it has become clear that microbes/ biofilms do not only cause corrosion, but they can also inhibit or protect against corrosion, which is so-called microbiologically influenced corrosion inhibition (MICI). The MIC efficiency is affected by diverse microbial species in biofilms and by different environmental conditions along with multiple types of interfacial media, and by the materials composition and surface characteristics.