To better understand the complex matter of Microbial Influenced Corrosion (MIC), it is pivotal to know the most common terms related to MIC. This article will walk you through the 17 commonly used MIC terms.
1. What is MIC?
Firstly, and probably the most used term: MIC. What does MIC stand for? MIC stands for Microbial Influenced Corrosion. This catch-all term defines all biological activity that result into loss of iron (Fe). There are many different species that can influence metals. However, there are two main mechanisms that will lead to the loss of iron. These mechanisms are CMIC or EMIC.
Chemical microbially influenced corrosion or CMIC occurs through the formation of corrosive components, such as organic acids, which stimulate the corrosion of iron. So there is stimulation of the cathodic reaction by metabolic end products, e.g. Hydrogen sulfide (H2S). The H2S formed will then corrode the iron.
Electronically Microbiological Influenced Corrosion (better known as EMIC). There are several mechanisms under this heading. Ultimately, with the same goal: to use electrons from iron. EMIC differs from CMIC in that it directly influences electron transfer at the surface of a metal. Whereas CMIC depends on chemical processes that take place between the microorganisms and the metal, with EMIC the microorganisms take control.
4. What is DNA?
DNA is the abbreviation of Deoxyribonucleic acid. This is the molecule in every living organisms that caries the most genetic instructions. This is central to the development, the functioning and reproduction of an organism.
5. What are Bacteria?
Bacteria are part of the so called ‘three-domain system’. This system is a biological classification introduced in 1990 and divides all the cellular life forms into three domains represented in a tree. The phylogenetic tree is based on RNA data and represents the evolutionary relationships among all organisms. The domain ‘Bacteria’ are any of the unicellular microorganisms, who are genetically distinct from the two other trees of life: Archaea and Eukaryotes.
6. What are Archaea?
Archaea are also part of the three-domain system. The Archaea are also unicellular microorganisms, which often live in extreme environmental conditions. Usually conditions where human beings can’t survive. Genetically, they are different from Bacteria and Eukaryotes.
7. What does ATP mean?
ATP stands for the molecule ‘Adenosine triphosphate’ and is the universal carrier of chemical energy of all living cells. ATP is an organic compound which is crucial for the energy cycle within every living organism. This molecule can be measured to provide an indicator about general biological activity.
8. What does the term ‘MMM methods’ refer to?
This refers to Molecular Microbiological methods and points to molecular analytical methods to characterize elements of biology. It’s thereby an umbrella term that can contain many different analytical technologies. In relation to MIC, the most recent techniques that are categorized under this definition are: Direct sequencing, Next generation Sequencing, FISH, DGGE and qPCR.
9. What is H2S?
This molecule is defined as Hydrogen Sulfide, a toxic and highly corrosive substance. Hydrogen Sulfide can have a biological source (being produced by SRB’s) or be a result of a chemical reaction.
10. What is qPCR?
qPCR stands for quantitative polymerase chain reaction. This technique copies targeted regions of the genome (DNA or RNA) to measure specific properties or parts of the genome. This has become a common technique to measure and quantify specific targets. These targets can be selected based on the design of a primer set.
11. What is a Primer (set)?
A ‘primer set’ is defined as at least one forward and one reverse primer. In practice, it can contain more than just one forward and reverse primer. Both the forward and reverse primer have a complementary sequence to the selected target sequence. This allows the amplification of DNA copies from this selected sequence through the PCR process.
12. What are SRB’s?
SRB stands for Sulfate reducing bacteria. This represents a common group of bacteria that are associated to influence the corrosion process by the formation of H2S or by direct electron uptake from the metal surface. Curious whether SRB’s can cause corrosion? In our article ‘Are Sulphate reducing organisms(SRB) causing corrosion?‘ we explain about SRB’s. However, SRB’s are not the same as MIC. The following article will clarify about the differences between SRB’s and MIC.
13. What are SRP’s?
This term stands for sulfate-reducing prokaryotes (SRP). In this definition both sulfate reducing organisms from the group of bacteria and Archaea are included.
14. What are SOB’s?
This is the common abbreviation for Sulpher oxidizing bacteria. SOB’s are the counterpart to SRB’s. Contrary to other organisms, they use the reversed Krebs cycle and use sulfur compounds as their starting point.
15. Taxonomic coverage, is this relevant?
Taxonomic coverage stands for the number of species that are detected with a primer for either qPCR or amplicon based sequencing. It is then defined as the number of species that are detected in relation to the total target of species.
16. What is a swab?
This is a small cotton-tipped stick that can be used for the sampling of surface areas. This approach can be used to sample sessile bacteria attached to the surface.
17. What is NGS?
Next Generation Sequencing (NGS) is a term that refers to different technologies that are capable to identify genetic fragments. The most commonly used approach within biomonitoring is to amplify a specific region before sequencing. Usually, the 16s rRNA general bacteria is being used to identify all the present microorganisms in a sample.
18. What is MicH?
MicH is the term that refers to a biomarker that targets the so called ‘Mic island’, this very distinctive genetic area from the gene of specific methanogens is responsible for EMIC driven corrosion processes. This EMIC process is not taking place within the cell from a methanogen, but externally. Through the so-called extracellular hydrogenasis. You can find MicH within the list of possible biomarker targets for qPCR. This biomarker gene is considered to have a very high correlation with the presence of corrosive biofilms in industrial systems.