Glossary of Terms

Glossary of Terms

Total BacteriaA summary count of all the bacteria in a sample
Total archaeaA summary count of all the archaea in a sample.
Quality ControlsInternal DNA controls are used to ensure accurate and precise qPCR quantification
Sulfate reducing bacteria
Sulfate reducing bacteria (SRB) gain energy for growth by reducing sulfate(SO42-) to sulfide (H2S). Sulfide production can cause souring of a system

SRB can also cause MIC by directly removing electrons from steel surfaces, and indirectly by producing corrosive by-products such as sulfide which react with iron to produce iron sulfide (FeS) deposits.
MethanogensThese anaerobic Archaea produce methane during their metabolism

Can lead to MIC by removing electrons directly from steel surfaces or indirectly through syntrophic interactions with other microbes
Iron oxidizing bacteria
Iron oxidizing bacteria (IOB) gain energy for growth by oxidizing ferrous iron (Fe2+) to ferric iron (Fe3+), resulting in the formation of ferric iron oxides on the steel surface

These oxides can be a protective physical barrier preventing any further corrosion, however they also result in the formation of oxygen depleted zones leading to electrochemical alterations of the steel surface, and localized, pitting corrosion
Iron reducing bacteria
Iron reducing bacteria (IRB) gain energy for growth by reducing ferric iron (Fe3+) to ferrous iron (Fe2+)

Fe3+ reduction can remove protective oxide coatings, exposing the surface beneath to further corrosion
Thiosulfate reducing bacteriaA sulfide producing microbe, increasingly common to oil and gas reservoirs stimulated by hydraulic fracturing methods

Sulfide production occurs via the use of thiosulfate and not sulfate, making this microbe a non-traditional SRB, undetectable by culture media bottle methods

Sulfide production poses both a souring and corrosion-based risk
Acid producing bacteria
Many bacteria form different organic acids during their metabolism, these acids can lead to corrosion of metal surfaces
Sulfur CyclingA broad spectrum qPCR target evaluating the genetic capacity for microbial conversion of sulfur related compounds

Supplementary to the total SRB qPCR primer set, the presence of “sulfur cycling” genes indicates a potential for microbial souring and/or MIC
Sulfur Oxidizing BacteriaA qPCR primer targeting the oxidation of sulfur-related compounds (sulfide, sulfur, thiosulfate) to sulfate.

Often considered a beneficial group of microbes as they function to remove sulfide (H2S) from a system, and are stimulated (used) in nitrate injection strategies for souring control. Recent research has indicated select SOB species can cause MIC by oxidizing sulfide to sulfuric acid (H2SO4).
Nitrate reducing bacteriaNitrate reducing bacteria (NRB) gain energy for growth by reducing nitrate to nitrite

Nitrate reduction is energetically favourable – NRB can outcompete SRB for growth on the same organics

Nitrite is itself corrosive, but is also a potent inhibitor of SRB
Slime producing bacteria
Many microbes prefer to live in a sessile community known as a biofilm

Biofilms are held together by a viscous slime or “extracellular matrix”

Some microbes produce particularly large amounts of slime when growing as a biofilm, and therefore pose a proportionately greater risk to biofouling or clogging events
SouringOilfield souring is a phenomenon whereby oil or gas reservoirs are made “sour” by the presence of hydrogen sulfide, H2S. The sulfide source can be non-biogenic (sulfur containing deposits in the reservoir), but is often a result of sulfide producing bacteria (biogenic sulfide).
16S16S is an rRNA gene found universally in all microbes (it encodes for highly important protein building machinery) that is analogous to a fingerprint – it can be used to identify the microbe(s) down to the species level. The 16S gene can be used in several molecular MIC tests
ArchaeaA domain of microorganisms (microbes) very similar, yet distinct from bacteria.
ATPAdenosine Triphosphate or ATP is the energy currency of cells. All cells (microbe or even human) use energy in the form of ATP to do work.
BacteriaSingle cell, microscopic organisms. Bacteria are found everywhere (capable of living under a very wide range of habitats including extreme environments).
GeneA functional region/unit of DNA within an organism (microbe). Genes have codes to make proteins that provide a specific function to the microbe. Example, the dsrAB gene(s) codes for proteins that are used in sulfate reduction by SRB.
MetagenomicsSequencing all of the 16S genes (reading all of the fingerprints) in a sample gives a list of all the microbes present, along with relative abundance percentages (semi-quantitative assay).
MICMicrobiologically Influenced Corrosion (MIC) describes the corrosive damage to surfaces caused by microbes, including bacteria and archaea.
MicrobeA unifying term used to describe bacteria and archaea (microscopic, unicellular organisms).
MMMMolecular Microbiological Methods (MMM) are culture-independent, genetic-based assays for MIC diagnostics.
qPCRQuantitative Polymerase Chain Reaction (qPCR) is a molecular microbiological method (MMM) that functions by counting/enumerating instances of a gene of interest in a given sample. For example, by counting the number of 16S genes in a sample, one can quantify the total number of microbes.
Sequencingsee metagenomics