Corrosion is generally thought of as a chemical process – so what have bacteria got to do with it? NCIMB’s Energy and Environmental Microbiology Services Manger, Michelle Robertson, gives an introduction to Microbiologically Influenced Corrosion and some methods used for monitoring the organisms involved.
Microorganisms are ubiquitous, occurring in all kinds of environments and they can quickly colonise the surfaces of man made structures, forming biofilms. Biofilms can be highly complex communities of different species with the early colonizers creating the conditions that allow others to follow, but the composition of communities varies from site to site. The figure below illustrates the stages and mechanisms that can be involved in biofilm formation. It also highlights the production of the extracellular polymeric substance matrix – a key characteristic of biofilms that provides structure and protects the cells within from environmental stresses – contributing to the difficulty of eradicating a well established biofilm.
The metabolic activity of microorganisms within biofilms can accelerate corrosion reactions on the surfaces that they colonise. This phenomenon is microbiologically influenced corrosion – sometimes also referred to as microbially influenced, or induced, corrosion, or MIC.
Microbiologically influenced corrosion accounts for a significant proportion of corrosion failures, and these failures can have serious consequences, so it is important that structures are monitored to assess their risk of being impacted by this common phenomenon. A number of different methods can be used for determining the presence of microorganisms that influence corrosion and three options are described below.
Monitoring method 1: most probable number
One approach is a culture-based enumeration known as the most probable number method or MPN. This method is based on the use of selective growth media to assess the presence of key groups of microorganisms commonly associated with microbiologically influenced corrosion.
As these groups of organisms each have different growth requirements the use of different selective growth media indicates which are present. As the name of this method suggests, the growth media is used, not only to indicate the presence or absence of different groups of microorganisms, but also to give an indication of the numbers present. This is done by creating a dilution series of sample in the media. The dilution at which no growth occurs can be used to estimate the number of microorganisms present in the original sample – the most probable number.
Monitoring method 2: qPCR
Another approach to monitoring the microorganisms involved in MIC is qPCR – something that the general public became much more familiar with during the COVID pandemic. This technique is used to quantify groups of microorganisms without any requirement for growth. It therefore gives rapid results, and ensures that microbes that do not grow under laboratory conditions are included in counts. This approach can be used to monitor the different groups of microorganism involved in microbially influenced corrosion to build a more in depth understanding.
Monitoring method 3: 16S sequencing
This technique, which has revolutionised understanding of environmental microbiology in recent years, analyses the whole microbial population from a single sample. It identifies the groups of microorganisms present to give a comprehensive picture of the microbial ecosystem within the sample site. This allows microbiological changes to be monitored in longitudinal studies as well as aiding understanding of the functional impact of the species observed. 16S community analysis is a powerful tool that can help assess the likelihood of corrosion.
If the presence of microorganisms known to influence corrosion is confirmed, then remedial action can be planned and its efficacy monitored with further sampling.
At NCIMB we supply speciality growth media for the main groups of organisms of concern with respect to microbiologically influenced corrosion. The range includes NACE-recommended recipes and our own proprietary formulations developed from our extensive experience of working with these groups of organisms. We also provide qPCR and 16S sequencing services for monitoring microorganisms that can influence corrosion. For more information visit our speciality media and oilfield microbiology web pages, or get in touch using the form below.