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Microbes, DNA and genome glossary of terms


The ribosome has two parts, which are called subunits. The RNA that makes up the small subunit (in bacteria) is called 16S and is often used as a marker for different types.


An organism is said to be aerobic if it needs oxygen to grow.


An organism is said to be anaerobic if it can grow without oxygen. Some organisms (called “obligate anaerobes”) can’t survive in the presence of oxygen; others (“facultative anaerobes”) can grow with or without. Many of the organisms that live in the human gut are anaerobes because there is very little oxygen.


A large group of microorganisms, often found in extreme environments, although some types also live in the human body. Their cells are very small and do not contain a nucleus (they are prokaryotes)


A very large group of microorganisms, the most common type found on the human body. Their cells are very small and do not contain a nucleus (they are prokaryotes).

Diversity Index

A measurement of the numbers and abundances of the different organisms in your environment. Usually (but not always) a higher diversity is beneficial. Can be calculated in a number of different ways.

DNA Sequencing

The DNA molecule is like a long string of chemical letters (G, A, T and C). Sequencing is reading out those letters, so that you can identify the piece of DNA and where it came from.


An unbalanced and unhealthy microbiome.


A balanced, healthy microbiome.


An organism whose cells have nuclei containing most of their DNA. Includes some micro-organisms (yeasts and protozoa) and larger organisms (all plants, animals and fungi).


An indigestible part of foods (especially plant-based foods) which are not digested, but are nonetheless very important for a healthy gut.


As well as mushrooms and toadstools, this group contains microbes including many types of yeasts. Their cells are larger than bacteria and Archaea and they are eukaryotes (they keep their DNA in a nucleus).


The complete DNA of an organism, containing all of its genes.

Gram stain

A stain that microbiologists use to tell different types of bacteria apart. Bacteria are said to be either gram-positive or gram-negative; the difference is the type of cell wall the bacteria have.


The genomes of all the organisms in a sample, taken together.


A microscopic form of life.


A microscopic form of life.


Either: 1. The community of microbes in an environment or 2. The DNA of those microbes.


The community of microbes in an environment that’s in or on a larger organism: for example, your gut or your skin.


A prebiotic is a substance in a food that encourages the growth of beneficial micro-organisms in the gut. They are typically complex sugars which make up part of the fibre in the diet.


Probiotics are live microbes which are believed to be beneficial when consumed. They are often found in products such as yoghurts or fermented foods, and are typically Lactobacillus or Bifidobacterium species. They are usually assumed to colonise the gut


An organism whose cells do not have nuclei. Includes the Bacteria and the Archaea.

Ribosomal DNA

The genes for the RNA that makes up the ribosome. Different groups of organisms have different ribosomal DNA sequences, which can be used to tell them apart.


A structure in a cell that makes the cell’s proteins. It is made of proteins and a molecule called RNA.

Learn more about these terms by downloading our full glossary here.