About this Research Topic
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 biocorrosion/ biodeterioration of materials and bioleaching of various minerals (mainly metal sulfide 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 behavior 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. Biocorrosion 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.
MIC by electro-active microbes is discussed to occur by an extracellular electron transfer (EET) - MIC. Microorganisms can obtain electrons by an extracellular oxidation of insoluble metals such as Fe0 with or without carrier molecules for the reduction of oxidants such as sulfate or nitrate inside the cytoplasm. For a thorough understanding of the mechanisms of biocorrosion electrochemical methods and omics techniques are used to macro/micro-analyze EET and interspecies electron transport of versatile microbial species as well as in interfacial interactions with materials.
This Research Topic aims to collect papers on recent advances on interfacial studies relevant to microbially catalyzed material (mineral and metal) dissolution processes. These include the chemical characterization of surface compounds for attachment and biofilm formation on mineral/metal surfaces, advanced microscopic studies of microorganism-material interactions as well as the in-situ characterization of the interfacial interaction-related elemental transformations and phase transitions of materials. Studies on the physiology and phylogeny of biomining/ biocorrosion microorganisms as well as recent omics data relevant to the understanding of the interfacial science are also welcome.
Keywords: Bioleaching, Biocorrosion, Attachment, Biofilms, Extracellular Electron Transfer